Process restart with `enumerateOnStartup` set to true causes all the notes getting synced again

If the `enumerateOnStartup` is set to `true` and process is restarted due to some issue, the entire enumeration process happens again (even for the already synced notes). 

The best way to do this is: 
- keep the metadata file always in-sync
- Verify the note's checksum with the metadata file's corresponding checksum for the file
- Sync only if the checksum is changed
