Zeitwerk simplifies working with dependencies in dev and makes it easier reloading class chains.
We no longer need to use Rails "require_dependency" anywhere and instead can just use standard
Ruby patterns to require files.
This is a far reaching change and we expect some followups here.
No need to let notifications stay around when users can't access
a topic after it was converted into a PM or posts were moved
into a restricted topic.
Also makes sure that moving to a new topic correctly uses the
guardian for the first post by enqueuing jobs outside of a
transaction.