This commit improves the performance and memory efficiency of `scripts/ci_validate_repo.py` by:
- Consolidating file discovery and multiple validation passes into a single iteration.
- Implementing an early size check using `pathlib.Path.stat().st_size` (metadata-only) to avoid opening large files.
- Using chunked binary reading (64KB chunks) for NUL byte detection to ensure a constant and low memory footprint regardless of file size.
- Adding "⚡ Bolt:" comments to document the performance improvements.