This patches add handling for unseen messages counter, and last message received. The
counters are retrieved from DB on startup, they updated in-memory. Frontend are expected
to have their own in-memory counter too, the backend one is used for re-sync (e.g.; on page
reload).
Bridge methods are added to retrieve the state, and indicate which message has been seen
last by user. A signal is sent on counter reset to all frontends can synchronise.
This is currently local only, but it should be compatible with a future XEP-0490 (Message
Displayed Synchronization) implementation.
Fix embedded bridge and adapt to changes in core code:
- Add `EmbeddedBridgeSettings` so it can be used in settings.
- Add `AIOBridge` and `TwistedBridge` wrappers.
- Fix callbacks, instead of logging them (and breaking the errback chain), they are now
raised using `BridgeException` like in other bridges.
- Ensure that a singleton `Bridge` is used between backend and frontend.
- Init backend on first call to `bridge_connect`.
- Add Python 3.14 fix (as it is normally done in Launcher which is not run with with
`embedded`, we have to do it there).
- Track generated files.
