[lib] assert message store equality after logout
Summary: Add missing check
Test Plan:
Log out and check if there are no errors.
Verify that all other checks are available:
- Go through all actions in the message reducer
- Analyze which of them are modifying messageStore.threads
- Confirm that ops are generated and state equality is checked
Reviewers: tomek, marcin, michal
Reviewed By: tomek
Subscribers: ashoat, atul
Differential Revision: https://phab.comm.dev/D7611