Add missing parse_benchmark_results.py script

The compare_benchmark_results.sh script was calling this file but it didn't exist.
This script:
- Parses baseline and PR CSV benchmark results
- Compares polars_bio performance against threshold
- Generates JSON and markdown reports
- Detects performance regressions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: mwiewior