Fixes #1911

Fixes #1911

Fix handling of "no-cpp" test tag for error tests, where "cpp" is already removed from the list of test backends.

Closes #3575

Fix handling of "no-cpp" test tag for error tests, where "cpp" is already removed from the list of test backends.

Closes #3575

Closes https://github.com/cython/cython/issues/3632

This avoids the METH_O function signature by default, since it does not match normal Python semantics.

* Fix unicode name handling of no-args functions when allowing keywords.

* Fix a crash when a keyword argument is passed to a function that does not allow them. Previously, the reported key name was not set and thus NULL.

* Extend "always_allow_keywords" test to cover some edge cases.
Some are commented out as they currently only work with the fastcall implementation.

See https://github.com/numpy/numpy/pull/16266

Use a more efficient way to check for PyCFunction and CyFunction at the same time since checking for PyCFunction became more costly in Py3.9.

Use an inlined version of PyType_HasFeature() instead of directly accessing "tp_flags" in the generated code.

See https://github.com/cython/cython/issues/3625