Refactor test_weighted_comparisons_plots.py for improved readability and reduced CCN

Summary:
## Summary:
This diff improves the test file `test_weighted_comparisons_plots.py` by refactoring tests for better readability, maintainability, and reduced cyclomatic complexity.

**Key improvements:**

1. **Enhanced Test Documentation:**
   - Added comprehensive docstrings to all test methods explaining their purpose and functionality
   - Improved method naming to be more descriptive (e.g., `test_plot_bar_weighted_comparison`, `test_plotly_marker_color_combinations`)
   - Added clear comments within test methods to explain test steps and assertions

2. **Code Organization:**
   - Consolidated helper functions to only include those used multiple times
   - `_create_concentrated_weight_test_data()` - used for edge case testing with concentrated weights
   - `_create_basic_test_dataframe()` - used across multiple frequency table tests
   - Moved helper functions to the top of the class for proper definition order

3. **Improved Test Structure:**
   - Refactored test methods to have clearer setup, execution, and assertion phases
   - Added descriptive variable names and inline comments for better readability
   - Enhanced test coverage documentation within docstrings

4. **Code Quality:**
   - Reduced cyclomatic complexity by eliminating unnecessary abstractions
   - Improved maintainability by following the principle of creating helpers only when genuinely reused
   - Maintained 100% functional compatibility - all original test logic preserved

**Testing Results:**
- All 220 tests pass successfully with no failures
- Build completes without errors
- Code formatting and linting pass cleanly

The refactoring maintains identical test behavior while significantly improving code clarity and maintainability.

# INTERNAL
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Reviewed By: atavory

Differential Revision: D78629315

fbshipit-source-id: 1d0508c20158e94729d93ca537c51770c6858a25

Author: talgalili