Add unittests for supervision.annotators.core module

[Borda]

Before submitting

• Self-reviewed the code
• Updated documentation, follow Google-style
• Added docs entry for autogeneration (if new functions/classes)
• Added/updated tests
• All tests pass locally

Description

just adding new tests to improve stability and test coverage

Type of Change

• 🧪 Test update

Testing

• I have tested this code locally
• I have added unit tests that prove my fix is effective or that my feature works
• All new and existing tests pass

Additional Notes

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Part of #2108

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58%. Comparing base (06bd638) to head (f886d75).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #2093    +/-   ##
========================================
+ Coverage       52%     58%    +7%     
========================================
  Files           61      61            
  Lines         7076    7076            
========================================
+ Hits          3657    4132   +475     
+ Misses        3419    2944   -475     

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[Copilot]

Pull request overview

This PR adds comprehensive unit tests for the supervision.annotators.core module to improve code stability and test coverage. The new test file covers 20 out of 23 annotator classes with basic functionality tests including empty detection handling and single detection annotation.

Changes:

• Added new test file test/annotators/test_core.py with 532 lines of test code
• Implemented test fixtures for test images, masks, and gradient images
• Created helper function assert_image_mostly_same for verifying annotation output

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