Fix lifecycle teardown in tracking node (#107)

- Store message_filters subscribers as class members so they can be cleaned up correctly
- Fix on_deactivate() to destroy the correct subscriptions and synchronizer
- Prevent AttributeError during lifecycle transitions

Author: ZeevBelinsky

yolo_ros/yolo_ros/tracking_node.py

@@ -105,15 +105,15 @@ def on_activate(self, state: LifecycleState) -> TransitionCallbackReturn:
         )
 
         # Subs
-        image_sub = message_filters.Subscriber(
+        self.image_sub = message_filters.Subscriber(
             self, Image, "image_raw", qos_profile=image_qos_profile
         )
-        detections_sub = message_filters.Subscriber(
+        self.detections_sub = message_filters.Subscriber(
             self, DetectionArray, "detections", qos_profile=10
         )
 
         self._synchronizer = message_filters.ApproximateTimeSynchronizer(
-            (image_sub, detections_sub), 10, 0.5
+            (self.image_sub, self.detections_sub), 10, 0.5
         )
         self._synchronizer.registerCallback(self.detections_cb)