refactor(benchmark): improve summary table logic, add CSV export

- Refactored summary table construction with `_build_summary_df` for cleaner, reusable logic.
- Added `save_results_csv` to export summary results as CSV.
- Expanded console width and refined column formatting for better readability.
- Adjusted table layout for improved compression ratio and operation speedup readability.
- Enhanced final output to display saved CSV location.