Improve file system event filtering performance for ignored paths

[eamodio]

Improves performance of file system event filtering for Git-ignored paths.

Summary

• Switches from async per-event ignore checking to sync filter function
• Buffers events during initial Git ignore rule loading
• Auto-refreshes filter when .gitignore or exclude files change
• Moves filtering earlier in the event pipeline

Impact

Users with large repositories or many ignored files experience reduced overhead from file system watching.

Validation

1. Open a large repository with many ignored files
2. Monitor CPU/memory usage during file operations
3. Verify improved responsiveness compared to previous behavior

Risk

Low - internal optimization with buffering to prevent event loss.