This commit optimizes the repository validation script (`scripts/ci_validate_repo.py`) by:
1. Combining the file size check and NUL byte check into a single pass over the file list.
2. Implementing chunked binary reading (64KB) for NUL byte detection to avoid loading entire files into memory.
3. Performing the size check before opening/reading the file to minimize redundant I/O.
These changes reduce memory overhead and improve execution efficiency during CI.
