feat: implement incremental asset caching in Chef
- Integrate MurmurHash3 for input-based cache key generation.
- Implement FuncCache for function-level memoization of asset cooking tasks.
- Add file tracking (path, size, mtime) to detect source asset changes.
- Refactor MeshAsset cooking to use incremental caching for collision shapes.
- Reduce game startup time to ~1.7s by avoiding redundant asset processing.
- Update .gitignore to exclude the new .chef/ cache directory.
- Update development journal with latest performance metrics.