`racetest` improvement

- Rename `TestGroup` -> `TestWorkGroup`. I originally named it as just
  WorkGroup similarly to sync.WorkGroup in pygolang, but later added
  "Test" prefix to highlight the difference that this class manages
  working group of threads that take part in tests, instead of group of
  arbitrary threads. However in that process I dropped the "Work" part
  which turned the name to be somewhat ambiguous: it is not clear whether
  "TestGroup" is a group of threads serving one test, or a group of
  separate tests without any relation to threading. To remove the
  ambiguity let's restore the "Work" in the name so that both "Test" and
  "WorkGroup" are there.

- Review test_racetest.py a bit:

  * make it a bit more robust by increasing "ok" timeout from 0.1s to 10s.
    in my experience 0.1s is too little and will regularly hit "timeout"
    when CI machines are overloaded. I'm still somewhat uncomfortable
    with 0.1s timeout we left in tests that exercise timeout handling,
    but let's leave it as is for now and see how it goes.

  * add test for cases when only one thread fails out of many, and when
    several threads fail too.

  * minor cosmetics.

- spellcheck.

Add the thread name to failure reports due to exceptions.
First update `TestGroup.threadv` before the thread is started.

- Factor common logic to spawn and run group of test threads into
  TestGroup. This way the extra checks and robustness improvements, that
  Dieter just added to check_race_external_invalidate_vs_disconnect,
  become available to all tests in racetest module.

  Rework moved code so that nwork is not fixed beforehand and test threads
  can be added dynamically.

- fix waiting logic in Finished:
  * on py2 Condition.wait does not return True/False as it does on py3 -
    we need to manually inspect the state.
  * fix race for when wait is called with already met condition:
    previously in such case it was waiting indefinitely and reporting
    failure on timeout

- rename Finished to well-established concept of WaitGroup and adjust
  its interface accordingly (see
  https://pkg.go.dev/sync#WaitGroup,
  https://lab.nexedi.com/nexedi/pygolang/blob/master/golang/sync.py and
  https://lab.nexedi.com/nexedi/pygolang/blob/39dde7eb/golang/sync.cpp#L153-200)

- no need to wrap try/except with additional try/finally, as
  try/except/finally works out of the box.

Corrected a few typos

Fix `racetest` problems

treat failure for a test thread to finish as a test failure

Add support for Python 3.11

Because `--all` takes precedence over any followup `-a X` on command
line in e.g. `tox -- -a 1`. See

    https://github.com/zopefoundation/ZEO/commit/06f8e1461c05

and

    https://github.com/zopefoundation/ZEO/pull/210#pullrequestreview-1094352596

for details.

/reviewed-by @d-maurer
/reviewed-on https://github.com/zopefoundation/ZODB/pull/368

As suggested by @d-maurer:

https://github.com/zopefoundation/ZODB/pull/368#issuecomment-1233198328
https://github.com/zopefoundation/ZODB/pull/368#issuecomment-1233245299

@d-maurer suggested to use more specific name fow interface describing
model specifications:

https://github.com/zopefoundation/ZODB/pull/368#discussion_r946358653
https://github.com/zopefoundation/ZODB/pull/368#discussion_r946406075

He also noticed several places in the comments that were unclear:

https://github.com/zopefoundation/ZODB/pull/368#discussion_r946364961
https://github.com/zopefoundation/ZODB/pull/368#discussion_r946372400
https://github.com/zopefoundation/ZODB/pull/368#discussion_r946388329

Also fix my oversight where _check_race_xxx_vs_external_disconnect was
left named wrongly.

Suggested by @d-maurer: https://github.com/zopefoundation/ZODB/pull/368#pullrequestreview-1073526911

And add a way to run tests without long tests:

	zope-testrunner --at-level=1

will run tests without those marked as being long.

By default tox continues to run all tests.

Suggested by @d-maurer with the idea to be able to skip long tests that
are unlikely to fail during development:

https://github.com/zopefoundation/ZODB/pull/368#discussion_r946386969

This currently fails for ZEO (see Bug2 in
https://github.com/zopefoundation/ZEO/issues/209 for details):

    (z-dev) kirr@deca:~/src/wendelin/z/ZEO5$ ZEO_MTACCEPTOR=1 zope-testrunner -fvvvx --test-path=src -t check_race_external_invalidate_vs_disconnect
    /home/kirr/src/wendelin/venv/z-dev/bin/zope-testrunner traceio=True
    /home/kirr/src/wendelin/z/ZEO5/src/ZEO/StorageServer.py:51: DeprecationWarning: The mtacceptor module is deprecated and will be removed in ZEO version 6.
      'in ZEO version 6.', DeprecationWarning)
    Running tests at level 1
    Running .BlobAdaptedFileStorageTests tests:
      Set up .BlobAdaptedFileStorageTests in 0.000 seconds.
      Running:
     check_race_external_invalidate_vs_disconnect (ZEO.tests.testZEO.BlobAdaptedFileStorageTests) (1.889 s)

    Failure in test check_race_external_invalidate_vs_disconnect (ZEO.tests.testZEO.BlobAdaptedFileStorageTests)
    Traceback (most recent call last):
      File "/usr/lib/python2.7/unittest/case.py", line 329, in run
        testMethod()
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/racetest.py", line 357, in check_race_external_invalidate_vs_disconnect
        T2ObjectsInc2Phase())
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/util.py", line 400, in _
        return f(*argv, **kw)
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/racetest.py", line 446, in _check_race_xxx_vs_external_disconnect
        self.fail('\n\n'.join([_ for _ in failure if _]))
      File "/usr/lib/python2.7/unittest/case.py", line 410, in fail
        raise self.failureException(msg)
    AssertionError: T15: obj1 (6) - obj2(4) != phase (1)
    obj1._p_serial: 0x03ea4cc505486777  obj2._p_serial: 0x03ea4cc503413799  phase._p_serial: 0x03ea4cc505486777
    zconn_at: 0x03ea4cc505486777  # approximated as max(serials)
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4cc505486777  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4cc504a74099  next_serial: None
    zstor.loadBefore(phase, @zconn.at)      ->  serial: 0x03ea4cc505486777  next_serial: None
    zstor._cache.clear()
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4cc505486777  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4cc504a74099  next_serial: 0x03ea4cc506104155
    zstor.loadBefore(phase, @zconn.at)      ->  serial: 0x03ea4cc505486777  next_serial: 0x03ea4cc506104155

    T51: obj1 (6) - obj2(4) != phase (1)
    obj1._p_serial: 0x03ea4cc505486777  obj2._p_serial: 0x03ea4cc503413799  phase._p_serial: 0x03ea4cc505486777
    zconn_at: 0x03ea4cc505486777  # approximated as max(serials)
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4cc505486777  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4cc503413799  next_serial: None
    zstor.loadBefore(phase, @zconn.at)      ->  serial: 0x03ea4cc505486777  next_serial: None
    zstor._cache.clear()
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4cc505486777  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4cc504a74099  next_serial: None
    zstor.loadBefore(phase, @zconn.at)      ->  serial: 0x03ea4cc505486777  next_serial: None

We will need it in soon for the next test.

Suggested by @d-maurer.

Example failure before this patch:

    Failure in test check_race_load_vs_external_invalidate (ZEO.tests.testZEO.BlobAdaptedFileStorageTests)
    Traceback (most recent call last):
      File "/usr/lib/python2.7/unittest/case.py", line 329, in run
        testMethod()
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/racetest.py", line 200, in check_race_load_vs_external_invalidate
        return self._check_race_load_vs_external_invalidate(T2ObjectsInc())
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/util.py", line 400, in _
        return f(*argv, **kw)
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/racetest.py", line 304, in _check_race_load_vs_external_invalidate
        self.fail([_ for _ in failure if _])
      File "/usr/lib/python2.7/unittest/case.py", line 410, in fail
        raise self.failureException(msg)
    AssertionError: ['T3: obj1 (1)  !=  obj2 (24)\n', 'T4: obj1 (1)  !=  obj2 (24)\n', 'T5: obj1 (1)  !=  obj2 (24)\n', 'T6: obj1 (1)  !=  obj2 (24)\n', 'T7: obj1 (2)  !=  obj2 (24)\n']

Example failure after this patch:

    Failure in test check_race_load_vs_external_invalidate (ZEO.tests.testZEO.BlobAdaptedFileStorageTests)
    Traceback (most recent call last):
      File "/usr/lib/python2.7/unittest/case.py", line 329, in run
        testMethod()
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/racetest.py", line 202, in check_race_load_vs_external_invalidate
        return self._check_race_load_vs_external_invalidate(T2ObjectsInc())
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/util.py", line 400, in _
        return f(*argv, **kw)
      File "/home/kirr/src/wendelin/z/ZODB/src/ZODB/tests/racetest.py", line 307, in _check_race_load_vs_external_invalidate
        self.fail('\n\n'.join([_ for _ in failure if _]))
      File "/usr/lib/python2.7/unittest/case.py", line 410, in fail
        raise self.failureException(msg)
    AssertionError: T0: obj1 (1)  !=  obj2 (25)
    obj1._p_serial: 0x03ea4be4ea558066  obj2._p_serial: 0x03ea4be4eaac7077
    zconn_at: 0x03ea4be4eaac7077  # approximated as max(serials)
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4be4ea558066  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: None
    zstor._cache.clear()
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: None

    T2: obj1 (1)  !=  obj2 (25)
    obj1._p_serial: 0x03ea4be4ea558066  obj2._p_serial: 0x03ea4be4eaac7077
    zconn_at: 0x03ea4be4eaac7077  # approximated as max(serials)
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4be4ea558066  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: None
    zstor._cache.clear()
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: None

    T3: obj1 (26)  !=  obj2 (25)
    obj1._p_serial: 0x03ea4be4ec6af5cc  obj2._p_serial: 0x03ea4be4eaac7077
    zconn_at: 0x03ea4be4ec6af5cc  # approximated as max(serials)
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4be4ec6af5cc  next_serial: None
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4be4eaac7077  next_serial: 0x03ea4be4ec962b00
    zstor._cache.clear()
    zstor.loadBefore(obj1, @zconn.at)       ->  serial: 0x03ea4be4ec6af5cc  next_serial: 0x03ea4be4ec962b00
    zstor.loadBefore(obj2, @zconn.at)       ->  serial: 0x03ea4be4ec6af5cc  next_serial: 0x03ea4be4ec962b00

Introduce the notion of testing model to represent initial state,
eveolution step and maintained invariant in the database.

Refactor tests to accept arbitrary such model and to drive them through
particular testing scenarious that try to hit specific concurrency
issues.

Not only this deduplicates the code a bit, but it also will allow us to
run different models through existing and future checkers. Soon we will
need to run a model with 3 variables (obj1, obj2 and phase) instead of
only 2 (obj1 and obj2) for invalidate / disconnect test.

Please see added module-level documentation for overview.