Make `StreamToken.room_key` be a `RoomStreamToken` instance. (#8281)

changelog.d/8281.misc

mypy.ini

synapse/handlers/admin.py

synapse/handlers/device.py

synapse/handlers/initial_sync.py

synapse/handlers/message.py

synapse/handlers/pagination.py

synapse/handlers/room.py

synapse/handlers/sync.py

synapse/notifier.py

synapse/storage/__init__.py

synapse/storage/databases/main/events.py

synapse/storage/databases/main/stream.py

synapse/storage/persist_events.py

synapse/types.py

tests/test_utils/event_injection.py