Enhance Codecov integration with token and test results upload

[bernardladenthin]

Summary

This PR improves the Codecov integration in the CI/CD pipeline by adding explicit token authentication and enabling test results upload to Codecov.

Key Changes

• Maven workflow: Added CODECOV_TOKEN secret to the existing codecov-action step for explicit authentication
• Maven workflow: Added new step to upload test results to Codecov using codecov/test-results-action@v1, which runs regardless of previous step outcomes
• README: Updated Codecov badge URL to use the new badge format with token parameter for better tracking and visibility

Implementation Details

• The test results upload step uses if: ${{ !cancelled() }} to ensure it runs even if previous steps fail, improving test visibility in Codecov
• Both Codecov actions now use the CODECOV_TOKEN secret for authenticated requests, which is more reliable than relying on GitHub context alone
• The badge update in README reflects the current Codecov badge format and includes the repository token for direct access

https://claude.ai/code/session_018e7Dax9ye4wXhF6MkKzrQ2

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.00%. Comparing base (b33f4bd) to head (b80f8a4).
⚠️ Report is 60 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #24      +/-   ##
============================================
+ Coverage     90.44%   97.00%   +6.56%     
- Complexity       41       47       +6     
============================================
  Files             1        1              
  Lines           157      167      +10     
  Branches         27       25       -2     
============================================
+ Hits            142      162      +20     
+ Misses            6        0       -6     
+ Partials          9        5       -4     

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