fix: apply loop factories for asyncio marks via parametrize

[l46983284-cpu]

Summary

In strict mode, pytest.mark.asyncio can be attached only to individual @pytest.mark.parametrize parameter sets (for example multi-backend tests). Collection already turns those async parameter sets into Coroutine items, but pytest_generate_tests only looked for a function-level asyncio marker. As a result, pytest_asyncio_loop_factories was never applied and the test kept the default event loop.

This change resolves the asyncio marker from parametrize parameter sets when the function itself has no asyncio marker, so configured loop factories still parametrize _asyncio_loop_factory.

Tests

• Regression: asyncio mark only via parametrize + custom loop factory (passed + skipped non-asyncio set).
• Review residual: multi-backend parametrize with pytest.mark.asyncio and an analogous non-asyncio backend mark, asserting loop type in the test body (tests/test_loop_factory_parametrize_multi_backend.py). CI does not depend on pytest-trio; the second backend is a tiny inline plugin.
• Local:
  python -m pytest tests/test_loop_factory_parametrization.py::test_asyncio_mark_via_parametrize_uses_hook_loop_factories tests/test_loop_factory_parametrize_multi_backend.py::test_asyncio_and_analogous_backend_parametrize_uses_loop_factories -q
• House: python -m pyright pytest_asyncio/ clean on this head.

Fixes #1463

[codecov-commenter]

Codecov Report

❌ Patch coverage is 55.17241% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.39%. Comparing base (1975f90) to head (1e46cc2).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
pytest_asyncio/plugin.py	55.17%	6 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1509      +/-   ##
==========================================
- Coverage   94.50%   92.39%   -2.12%     
==========================================
  Files           2        2              
  Lines         510      539      +29     
  Branches       62       71       +9     
==========================================
+ Hits          482      498      +16     
- Misses         22       28       +6     
- Partials        6       13       +7     

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[tjkuson]

I don't think this test covers the failure described in #1463. I would expect this PR to include a test that is parametrized via both pytest.mark.asyncio and pytest.mark.trio (or something analogous) with an assertion on loop type within the test body.

[l46983284-cpu]

Thanks for the review — agreed the first regression was too narrow for the #1463 multi-backend shape.

I added test_asyncio_and_analogous_backend_parametrize_uses_loop_factories: one parametrize with pytest.mark.asyncio and an analogous non-asyncio backend mark, and loop-type asserts inside the test body. CI no longer depends on pytest-trio, so the second backend is a tiny inline plugin instead of a hard trio dep; with pytest-trio installed locally the same product path also passes the real trio pair.

Focused tests green on this head.