Add RoomInfo cache, remove RoomServerRoomNIDsCache (#1646)

* Add RoomInfo cache, remove RoomServerRoomNID cache, ensure caches are thread-safe

* Don't panic if the roomInfo isn't known yet

* LRU package is already threadsafe

* Use RoomInfo cache to find room version if possible in Events()

* Adding comments about RoomInfoCache safety

internal/caching/caches.go

@@ -10,6 +10,7 @@ type Caches struct {
 	RoomServerEventTypeNIDs Cache // RoomServerNIDsCache
 	RoomServerRoomNIDs      Cache // RoomServerNIDsCache
 	RoomServerRoomIDs       Cache // RoomServerNIDsCache
+	RoomInfos               Cache // RoomInfoCache
 	FederationEvents        Cache // FederationEventsCache
 }