Fix pylint errors in benchmark directory

[kenya-sk]

This PR addresses various Pylint errors in the benchmarks/ directory to ensure CI compliance and improve code quality. The changes include fixing import paths, enforcing naming conventions, and modernizing Python syntax.

• Fix Imports:
  • Converted relative imports to absolute imports (e.g., benchmarks.scripts...) and resolved test_log_pb2 import issues. Grouped imports to fix wrong-import-order and ungrouped-imports errors.
• Style & Formatting:
  • Renamed TEST_FLAGS to test_flags and converted test method names to snake_case (e.g., test_benchmark_gradient) to comply with PEP8 naming conventions.
  • Wrapped long lines and docstrings to satisfy the 80-character line length limit.
• Documentation:
  • Added missing module and function docstrings.
• Refactoring:
  • Updated super() calls to the cleaner Python 3 syntax (super().init()).

[mhucka]

@kenya-sk Thank you for this work and the PR. This all looks good; however, because we're in the middle of getting release 0.7.6 done, I will hold off on merging this until after the release.