Detect blocking calls in coroutines using BlockBuster

[cbornet]

Changes

This PR uses the blockbuster library to detect blocking calls made in the asyncio event loop during unit tests.
Avoiding blocking calls is hard as these can be deeply buried in the code or made in 3rd party libraries.
Blockbuster makes it easier to detect them by raising an exception when a call is made to a known blocking function (eg: time.sleep).

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) added which would fail without your patch
• You've updated the documentation (in docs/, in case of behavior changes or new
  features)
• You've added a new changelog entry (in docs/versionhistory.rst).

If there's no issue linked, just link to your pull request instead by updating the
changelog after you've created the PR.

[cbornet]

@agronholm about your question if it would have detected the iterdir issue: it would have.
I did on my local with Python 3.13 venv

git revert 38885f9
pytest "tests/test_fileio.py::TestPath::test_iterdir[asyncio]"
=================================================================== test session starts ====================================================================
platform darwin -- Python 3.13.2, pytest-8.3.4, pluggy-1.5.0
rootdir: /Users/christophe.bornet/workspace/anyio
configfile: pyproject.toml
plugins: anyio-0.0.post1087+dirty, hypothesis-6.126.0
collected 1 item

tests/test_fileio.py F                                                                                                                               [100%]

========================================================================= FAILURES =========================================================================
______________________________________________________________ TestPath.test_iterdir[asyncio] ______________________________________________________________
tests/test_fileio.py:409: in test_iterdir
    async for path in Path(populated_tmpdir).iterdir():
src/anyio/_core/_fileio.py:548: in iterdir
    gen = self._path.iterdir()
../../.pyenv/versions/3.13.2/lib/python3.13/pathlib/_local.py:576: in iterdir
    paths = [entry.path for entry in scandir_it]
.venv/lib/python3.13/site-packages/blockbuster/blockbuster.py:109: in wrapper
    raise BlockingError(func_name)
E   blockbuster.blockbuster.BlockingError: Blocking call to ScandirIterator.__next__

[agronholm]

There are test failures still. I'll take another look after you've fixed them.

[agronholm]

There are test failures still. I'll take another look after you've fixed them.

Oh, sorry, these are caused by the calls you asked about. Never mind.

[agronholm]

By the way, I suggest you refrain from force-pushing. It makes it harder to track the incremental changes you're making.

[agronholm]

Are you sure you're not adding exemptions for legit errors reported by this tool?

[cbornet]

By the way, I suggest you refrain from force-pushing. It makes it harder to track the incremental changes you're making.

Sorry about that. Some commit/pushs I have done were to figure out how to fix. I was using the CI to test because I don't have a Windows machine to test locally.

[cbornet]

Are you sure you're not adding exemptions for legit errors reported by this tool?

Yes. These errors are maybe legit reports. I've put them as exemptions for now so we can discuss how to fix them.

[agronholm]

Thanks!

[cbornet]

Awesome, thanks !