CI: run tests in Matrix and upload only 3.12 to Codecov

[shenanigansd]

No description provided.

[codspeed-hq]

Merging this PR will improve performance by 10.23%

⚡ 1 improved benchmark
✅ 1 untouched benchmark

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_stutter[1.0-I love dogs-I l-love d-dogs]	130.3 µs	118.2 µs	+10.23%

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_{Comparing br/matrix-but-codecov (6339294) with main (20c05c8)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.29%. Comparing base (20c05c8) to head (6339294).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #137   +/-   ##
=======================================
  Coverage   88.29%   88.29%           
=======================================
  Files           3        3           
  Lines          94       94           
=======================================
  Hits           83       83           
  Misses         11       11           

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[Copilot]

Pull request overview

This PR refactors the CI workflow to separate linting and testing into distinct jobs, implements a test matrix for Python versions 3.10-3.14, and optimizes Codecov uploads to only include Python 3.12 coverage reports.

Changes:

• Split the lint-test job into separate lint and test jobs for better parallelization
• Added a test matrix to run tests across Python versions 3.10, 3.11, 3.12, 3.13, and 3.14
• Created a separate codecov job that downloads and uploads only Python 3.12 coverage and test results to Codecov

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

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[Copilot]

The PR title indicates that coverage from Python 3.12 should be uploaded to Codecov, but this downloads coverage from Python 3.14 instead. This should be changed to "coverage-py3.12" to match the PR's stated intent.

Suggested change

	name: coverage-py3.14
	name: coverage-py3.12

[Copilot]

The codecov job uses "if: always()" which means it will run even if the test job fails. However, the download-artifact step uses "if: !cancelled()" which may cause issues if the test job fails and no artifact is produced. Consider adding a check to ensure the artifact exists before attempting to download, or adjust the condition to handle cases where tests fail for Python 3.12.