Set default asyncio fixture loop scope to function

[SahilArchitect]

Closes #924.

Summary

Sets the default value of asyncio_default_fixture_loop_scope to function and removes the deprecated unset
fallback/warning path.

This intentionally only changes the default for async fixture loop scope. It does not change async test loop scope
behavior, custom event_loop fixture deprecations, pytest warning filtering order, or quoted pytest.ini value
parsing.

Changes

• Default unset asyncio_default_fixture_loop_scope to function
• Remove the old fallback to fixture caching scope
• Update docs and changelog wording
• Add regression coverage for the unset/default behavior

Tests

• python -m pytest tests/test_fixture_loop_scopes.py
• python -m pytest tests/test_asyncio_fixture.py tests/modes/test_auto_mode.py tests/modes/test_strict_mode.py

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.87%. Comparing base (74a5557) to head (6b37a20).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1444      +/-   ##
==========================================
+ Coverage   94.50%   94.87%   +0.36%     
==========================================
  Files           2        2              
  Lines         510      507       -3     
  Branches       62       61       -1     
==========================================
- Hits          482      481       -1     
+ Misses         22       21       -1     
+ Partials        6        5       -1     

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[seifertm]

Thanks for the initiative, @SahilArchitect .

This is a breaking change that requires a major version bump. The next version will be v1.4.0, so I won't merge the PR just yet. In the meantime, could you have a look at my comments?

[seifertm]

The news fragment describes a change of a warning message. Your change is unrelated to this news fragment and will be included in a different release. Please remove any modifications to this file.

[seifertm]

This is the migration guide for users looking to upgrade from an older version of pytest-asyncio. This patch doesn't change anything in the upgrade path. Please remove any modifications to this file.

[SahilArchitect]

Thanks for the review. I pushed a follow-up commit now.

What I changed:

• restored changelog.d/1298.changed.rst, since that was for the older warning-message change
• restored both migration guide files, since this PR does not need to change those upgrade docs
• updated the regression test so it now actually proves the unset default is using function

For the test: I changed it to use a scope="module" async fixture with no explicit loop_scope. With the old behavior, that would fall back to the module fixture scope and pass. With the new behavior, it tries to use _function_scoped_runner, so we get the expected ScopeMismatch. That makes the behavior difference visible in the test.

I also reran:

.venv/bin/python -m pytest tests/test_fixture_loop_scopes.py -q
.venv/bin/python -m pytest tests/test_asyncio_fixture.py tests/modes/test_auto_mode.py tests/modes/test_strict_mode.py -q

Both passed.