[SYSTEMDS-3427] CodeCoverage Python

[aperov9]

This pull request introduces test coverage reporting for the Python-based code base & uploads the merged coverage to codecov.

CI/CD and Coverage Reporting Enhancements

• Updated the Python workflow to install the coverage package, run tests with coverage enabled for all test modes (including federated and scuro), and collect per-mode coverage data files. Added a new job to merge these coverage files, generate a combined report, and upload it to Codecov and as workflow artifacts.
• Modified the Java test workflow to tag Codecov uploads with a java flag for clearer separation of coverage data.
• Please make sure to enable the flag feature in codecov.

Documentation and Badge Updates

• Updated the README.md to display separate Codecov badges for Java and Python coverage.

Python Coverage Configuration

• Added a .coveragerc configuration file in src/main/python to omit irrelevant files (such as those generated by OpenCV and PyTorch) from coverage analysis.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 14.85%. Comparing base (3779d50) to head (f223388).

❗ There is a different number of reports uploaded between BASE (3779d50) and HEAD (f223388). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (3779d50)	HEAD (f223388)
	1	0

Additional details and impacted files

@@              Coverage Diff              @@
##               main    #2359       +/-   ##
=============================================
- Coverage     72.33%   14.85%   -57.49%     
+ Complexity    46911     5635    -41276     
=============================================
  Files          1513     1912      +399     
  Lines        178198   191807    +13609     
  Branches      34984    34984               
=============================================
- Hits         128897    28489   -100408     
- Misses        39556   159790   +120234     
+ Partials       9745     3528     -6217     

Flag	Coverage Δ
java	9.70% <ø> (?)
python	82.26% <ø> (?)

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🚀 New features to boost your workflow:

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