feat(health): optimize library sync for large libraries

[drondeseries]

Description

This PR optimizes the library sync process to handle large libraries (15k+ files) more efficiently, especially when using network mounts (rclone).

Key Changes

• Streaming Batch Additions: Instead of collecting all new files in a large slice in RAM, records are now processed and inserted into the database in batches of 1,000 as they are discovered. This significantly reduces the memory footprint.
• Improved Filesystem Performance: Switched from filepath.Walk to filepath.WalkDir for metadata scanning to avoid unnecessary os.Lstat calls.
• Progress Visibility: Added periodic log messages every 1,000 files during scanning and processing phases to provide feedback during long syncs.
• Minor Optimizations: Moved path cleaning outside of loops in filesystem walk functions.