chore: modernize Python test config and setup

[RyukR1]

Description

This PR resolves configuration issues and runtime errors encountered when executing Python-based integration/unit tests on newer Python (3.12/3.13) and Setuptools (>= 72) environments.

Changes

1. Migrate pytest Config: Renamed the deprecated [pytest] section header to [tool:pytest] in both tests/setup.cfg and tests/unit/setup.cfg to align with modern pytest standards.
2. Ignore Legacy Warnings: Added filterwarnings = ignore::DeprecationWarning to ignore distutils.version.LooseVersion deprecation warnings caused by non-PEP440 versions (e.g., 3.9.0-SNAPSHOT).
3. Remove Deprecated Test Command: Cleaned up the custom PyTest wrapper class in tests/setup.py that inherited from the deprecated/removed setuptools.command.test class (avoiding runtime RuntimeError on Setuptools 72+).
4. Update Documentation: Updated the tests/README.md to guide developers to run pytest directly and corrected folder reference paths (kafka/tests/ -> tests/).

Verification

• Checked unit tests locally: pytest executed inside the tests/ directory with 6/6 tests passing successfully.
• Ran project checkstyle/formatting/licensing checks: ./gradlew rat checkstyleMain checkstyleTest spotlessJavaCheck completed successfully.

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