Include saved mtime and fingerprint when serializing buffers

This still doesn't include:

- An assertion in the randomized test to ensure buffers are not spuriously
marked as modified
- Sending an update when synchronizing buffers after a reconnection
467e5691b9Antonio Scandurra committed on 1/17/2023, 9:46:19 AMparent6251518
2 files changedLine totals unavailable