Optimized `scripts/ci_validate_repo.py` for better performance and lower memory usage:
- Combined NUL byte and size checks into a single pass over files.
- Implemented chunked binary reading (64KB chunks) for NUL byte detection, avoiding full file loads into RAM.
- Reused `stat()` results to minimize redundant system calls.
- Added early exit for large files before performing content checks.
These changes make the repository validation process faster and more efficient, especially in CI environments.
