ci: upload coverage to Codecov

[nficano]

Summary

• Upload the Jacoco XML reports (already produced by every java-library subproject; see build.gradle.kts:36-46) to Codecov.
• Uploaded only from the JDK 21 LTS matrix entry — same source coverage on every JDK.
• fail_ci_if_error: false so a Codecov outage cannot break CI.

Pre-merge action required

• Add CODECOV_TOKEN as a repo secret (gh secret set CODECOV_TOKEN --repo agentruntimecontrolprotocol/java-sdk).
• Activate the repo at app.codecov.io.

Test plan

• Merge, confirm coverage uploads on next push to main.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Enhanced continuous integration workflow to automatically upload code coverage reports.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: a31dbfe8-23d3-4220-a914-439a301dc32c

📥 Commits

Reviewing files that changed from the base of the PR and between e0aeadf and fbb6708.

📒 Files selected for processing (1)

• .github/workflows/ci.yml

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Walkthrough

The PR adds a conditional Codecov upload step to the CI workflow that runs only on JDK 21. It uploads JaCoCo coverage reports to Codecov with documentation, token authentication, and non-failing error handling to avoid blocking CI on upload failures.

Changes

CI Coverage Upload

Layer / File(s)	Summary
Codecov upload step for JDK 21 .github/workflows/ci.yml	Adds documentation comments and a conditional Upload coverage to Codecov step that runs when matrix.jdk == '21'. Configures the pinned codecov/codecov-action to upload the JaCoCo XML report with the unittests flag, passes the Codecov token, and sets fail_ci_if_error: false to prevent build failures on upload errors.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'ci: upload coverage to Codecov' directly and clearly describes the main change—adding a CI step to upload coverage reports to Codecov.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ 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-upload

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