* Make backfill work for shared history visibility
* fetch missing state on backfill to remember snapshots correctly
* Fix gmsl to not mux in auth events into room state
* Whoops
* Linting
* Implement history visibility checks for /backfill
Required for p2p to show history correctly.
* Add sytest
* Logging
* Fix two backfill bugs which prevented backfill from working correctly
- When receiving backfill requests, do not send the event that was in the original request.
- When storing backfill results, correctly update the backwards extremity for the room.
* hack: make backfill work multiple times
* add sqlite impl and remove logging
* Linting
