Migrate local actions to calysto/maintainer_tools

[blink1073]

References

N/A

Description

Replaces all local .github/actions/* composite actions with their equivalents from the shared calysto/maintainer_tools repository, referenced via the @v1 floating tag.

Changes

• Replace uses: ./.github/actions/base-setup → calysto/maintainer_tools/actions/base-setup@v1 in all workflow jobs
• Replace uses: ./.github/actions/test-sdist → calysto/maintainer_tools/actions/test-sdist@v1 and remove redundant preceding base-setup step (runs internally)
• Replace uses: ./.github/actions/test-minimum-versions → calysto/maintainer_tools/actions/test-minimum-versions@v1 and remove redundant preceding base-setup step (runs internally)
• Replace uses: ./.github/actions/release → calysto/maintainer_tools/actions/release@v1 and remove redundant preceding base-setup step (runs internally)
• Replace uses: ./.github/actions/enforce-label → calysto/maintainer_tools/actions/enforce-label@v1
• Delete .github/actions/ directory (6 files)
• Add calysto/maintainer_tools/actions/*: ref-pin to .github/zizmor.yml to allow ref-pinned usage of the shared actions

Backwards-incompatible changes

None

Testing

The dry-run release job in the test suite exercises the release action end-to-end on every PR.

AI usage

• This PR contains AI-generated content
• I have carefully reviewed the PR and run the code
• Tools/models used: Claude Sonnet 4.6 (Claude Code)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.30%. Comparing base (f8b882a) to head (5664e70).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #414   +/-   ##
=======================================
  Coverage   90.30%   90.30%           
=======================================
  Files          51       51           
  Lines        2950     2950           
  Branches      414      414           
=======================================
  Hits         2664     2664           
  Misses        209      209           
  Partials       77       77           

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