Add a type hint for get_device_handler() and fix incorrect types. (#14055)

This was the last untyped handler from the HomeServer object. Since
it was being treated as Any (and thus unchecked) it was being used
incorrectly in a few places.

synapse/replication/http/devices.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import logging
-from typing import TYPE_CHECKING, Tuple
+from typing import TYPE_CHECKING, Optional, Tuple
 
 from twisted.web.server import Request
 
@@ -63,7 +63,12 @@ class ReplicationUserDevicesResyncRestServlet(ReplicationEndpoint):
     def __init__(self, hs: "HomeServer"):
         super().__init__(hs)
 
-        self.device_list_updater = hs.get_device_handler().device_list_updater
+        from synapse.handlers.device import DeviceHandler
+
+        handler = hs.get_device_handler()
+        assert isinstance(handler, DeviceHandler)
+        self.device_list_updater = handler.device_list_updater
+
         self.store = hs.get_datastores().main
         self.clock = hs.get_clock()
 
@@ -73,7 +78,7 @@ class ReplicationUserDevicesResyncRestServlet(ReplicationEndpoint):
 
     async def _handle_request(  # type: ignore[override]
         self, request: Request, user_id: str
-    ) -> Tuple[int, JsonDict]:
+    ) -> Tuple[int, Optional[JsonDict]]:
         user_devices = await self.device_list_updater.user_device_resync(user_id)
 
         return 200, user_devices