Fixes #1920

Update to greenlet 2.0

Request this for the two IDNA cases, which somehow give different errors using the same resolver on GHA.

Its failing in a weird way that doesn't happen locally.

There is a remaining issue, which lies somewhere in greenlet, seen in
test__monkey_hub_in_thread and test__threading_monkey_in_thread:

  Fatal Python error: Python memory allocator called without holding the GIL

  Python runtime state: finalizing (tstate=0xd5f3e0)

  Thread 0x00007f511f66b700 (most recent call first):
  <no Python frame>

Obviously this mixes with threads. greenlet uses Py_AddPendingCall to
move some work to other threads, but apparently something is still
happening at the wrong time.

Fixes #1909

We'll need to release a final greenlet 2.0 and remove the rc qualifiers here before releasing gevent, because pre-release qualifiers are contagious.

Stop using DEF statements in Cython, as they are deprecated.

See https://github.com/cython/cython/issues/4310

Fixes #1914

Use the non-legacy `setuptools.build_meta` backend.  Prepend the setup
directory to `sys.path` prior to importing modules relative to it.

Fixes #1910

Remove redundant wheel dep from pyproject.toml

Libuv 1.44.2

Run leakchecks on Python 3.11; make them more comprehensive

They're important objects. Locally, the 3.11 tests pass fine this way.

The 2.7 tests had two failures, one from being unable to make a connection in test__server, and one from a timeout in test__doctest. I suspect those are unrelated; lets see what CI says.

Remove the redundant `wheel` dependency, as it is added by the backend
automatically.  Listing it explicitly in the documentation was
a historical mistake and has been fixed since, see:
https://github.com/pypa/setuptools/commit/f7d30a9529378cf69054b5176249e5457aaf640a