Check requires-mark coverage across CI runs

[officialasishkumar]

Description

Add a CI safeguard that uploads pytest-reportlog output from each test-matrix job and checks that tests skipped via requires_* markers are exercised somewhere in CI, unless the dependency gate is explicitly allowlisted as unsupported in GitHub Actions.

This also adds focused tests for the coverage checker script.

Checklist

• Closes Add CI to ensure all requires_ tests are run at least once #11273
• Tests added
• User visible changes (including notable bug fixes) are documented in whats-new.rst (N/A - internal CI change)
• New functions/methods are listed in api.rst (N/A - internal tooling change)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
    Tools: Codex

Test plan

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 python3 -m pytest -o addopts= /tmp/xarray-wt-11273/ci/test_check_requires_coverage.py -q

[VeckoTheGecko]

Hi @officialasishkumar , thanks for looking into this!

Hmmm. I was wondering whether in the original issue whether this can be explored using custom marks (whether that's something that Pytest supports). Have you looked into this @officialasishkumar ? Maybe that would be a way forward?

Solely grepping through error messages seems quite error prone/flaky and I don't know if that's the way we should be handling something as fundamental as determining if our test suite passes

Also, can you elaborate on how you tested this @officialasishkumar ? The test plan doesn't really make sense to me and the job was failing with many errors

[VeckoTheGecko]

cc @keewis since you were thinking along with me in the original issue

[VeckoTheGecko]

@officialasishkumar

I see that you've posted #11290, #11291, #11292, and this PR in very quick succession. Have you read through our AI policy? https://docs.xarray.dev/en/latest/contribute/ai-policy.html And can you confirm whether all of these contributions are in line with this policy?

This is a lot of PRs to go through and I want to make sure that maintainers time is being respected while reviewing these

[officialasishkumar]

hi @VeckoTheGecko , yes, i have gone through the AI policy