Refactor MQTT (#24010)

* refactor mqtt so that Frigate owns the transport lifecycle instead of delegating it to paho

* release the shutdown barrier on worker crash and replay retained publishes the broker never acked

* collapse in-flight retained values by topic and release the shutdown barrier from a finally

* replay the outage buffer before the publish queue so newer values are not reverted

frigate/comms/webpush.py

@@ -63,14 +63,8 @@ class WebPushClient(Communicator):
         self.last_notification_time: float = 0
         self.user_cameras: dict[str, set[str]] = {}
         self.notification_queue: queue.Queue[PushNotification] = queue.Queue()
-        self.notification_thread = threading.Thread(
-            target=self._process_notifications, daemon=True
-        )
-        self.notification_thread.start()
-        self.suspension_thread = threading.Thread(
-            target=self._process_suspensions, daemon=True
-        )
-        self.suspension_thread.start()
+        self.notification_thread: threading.Thread | None = None
+        self.suspension_thread: threading.Thread | None = None
 
         if not self.config.notifications.email:
             logger.warning("Email must be provided for push notifications to be sent.")
@@ -99,6 +93,16 @@ class WebPushClient(Communicator):
         """Wrapper for allowing dispatcher to subscribe."""
         pass
 
+    def start(self) -> None:
+        self.notification_thread = threading.Thread(
+            target=self._process_notifications, daemon=True
+        )
+        self.notification_thread.start()
+        self.suspension_thread = threading.Thread(
+            target=self._process_suspensions, daemon=True
+        )
+        self.suspension_thread.start()
+
     def check_registrations(self) -> None:
         # check for valid claim or create new one
         now = datetime.datetime.now().timestamp()
@@ -608,4 +612,5 @@ class WebPushClient(Communicator):
 
     def stop(self) -> None:
         logger.info("Closing notification queue")
-        self.notification_thread.join()
+        if self.notification_thread is not None:
+            self.notification_thread.join()