ci: add Codecov test analytics

[JohnRDOrazio]

Summary

• Adds --junitxml=junit.xml to pytest to generate JUnit XML test results
• Uploads test results to Codecov via codecov/test-results-action@v1
• Uses if: ${{ !cancelled() }} so results are uploaded even on test failures

Test plan

• CI passes and test results appear on Codecov dashboard

🤖 Generated with Claude Code

Summary by CodeRabbit

• Documentation
  • Added Codecov coverage badge to the README.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

These changes integrate Codecov test results reporting into the release workflow by adding JUnit XML output to pytest and a new Codecov test results action, while adding a Codecov coverage badge to the README.

Changes

Cohort / File(s)	Summary
CI/Workflow Configuration .github/workflows/release.yml	Added --junitxml=junit.xml flag to pytest invocation and introduced codecov/test-results-action@v1 step with conditional execution to report test results to Codecov.
Documentation README.md	Added Codecov coverage badge linking to the repository's Codecov metrics page.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 A badge now shines, so bright and true,
Codecov's eye sees all we do,
Test results flow with JUnit's might,
Our coverage measured, crystal bright! 🌟

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the primary change: adding Codecov test analytics integration to the CI workflow.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/codecov-test-analytics

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!