Add grpc.experimental.gevent stubs

[wangting0128]

Changes

Add minimal stubs for grpc.experimental.gevent, which exists in the grpcio runtime package but is currently missing from the partial grpcio stubs.

This adds:

• stubs/grpcio/grpc/experimental/__init__.pyi
• stubs/grpcio/grpc/experimental/gevent.pyi
• a regression test case for importing grpc.experimental.gevent and calling init_gevent()

Follow-up to #15833.

Testing

python tests/runtests.py stubs/grpcio

Result:

--- TEST SUMMARY: All tests passed! ---

pre-commit Success
Check structure: Success
Pyright: Success
mypy: Success
stubtest: Skipped
Pyright regression tests: Success
mypy regression test: Success

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[brianschubert]

Thanks, see remarks below.

I'd normally be a little hesitant to add stubs for "experimental" APIs that may be removed in any minor release, but this particular function seems pretty stable (8+ yerars) and there seems to be ongoing work to maintain it / gevent compatibility, so adding it feels fine to me.

[brianschubert]

You can remove this file - test cases are only needed for weird and/or complicated cases that might regress in the future. This test basically repeats the signature (and a particularly trivial one at that :-)), so it isn't really necessary

[brianschubert]

The runtime doesn't actually re-export gevent, so e.g. this fails:

$ uv run -w grpcio python3 -c 'import grpc.experimental; grpc.experimental.gevent'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import grpc.experimental; grpc.experimental.gevent
                              ^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: module 'grpc.experimental' has no attribute 'gevent'

Type checkers understand submodule relationships, so we don't need to add anything here in order for them to understand that the gevent submodule exists.

Suggested change

from . import gevent as gevent

[brianschubert]

I think you can just delete this file, since partial-stub = true, and no direct members of this module are being stubbed. But if that ends up not being the case, you need to add the following to account for the fact that not all public functions are part of the stub file:

def __getattr__(name: str): ...  # incomplete module

The partial-stub marker in METADATA.toml only tells type checkers that whole modules are missing, not that modules that do exist might be incomplete. That's what the __getattr__ does. You may also need to add this module to pyrightconfig.stricter.json if not already covered