[lib] Check the timestamps when updating read status for all the specs

Summary:
Only update the status when it is more recent than the saved timestamp.

https://linear.app/comm/issue/ENG-9112/handle-unread-status

Depends on D13234

Test Plan: Process a couple of operations with text messages and check if the unread status and timestamps are correct.

Reviewers: kamil, inka, marcin

Reviewed By: marcin

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13241