as /sync races with /send, and remote echo may happen first.
It's important for local echo that the pending redaction/relation
will also get attached to the remote echo before /send returns,
otherwise the remote echo would be "unannotated" until /send returns
Which we can then reuse to create a dedicated ArchivedRoom class
which will:
- have only relevant methods and properties (e.g. no sendEvent)
- turns out that you can still receive a leave room in the sync
(e.g. when banned after kick) so we'll make the sync for
an archived room separate from room to not overcomplicate the sync
there, much like we did for Invite already.
