fix(utilities): Ensure unique signal handlers for counter models

Updates `connect_counters` to prevent duplicate signal handlers by
using consistent `dispatch_uid` values per sender. Adds a check to
avoid reconnecting models already processed during registration.

Fixes #20697

Author: pheus

netbox/utilities/counters.py

@@ -77,7 +77,7 @@ def post_delete_receiver(sender, instance, origin, **kwargs):
         parent_pk = getattr(instance, field_name, None)
 
         # Decrement the parent's counter by one
-        if parent_pk is not None and not hasattr(instance, "_previously_removed"):
+        if parent_pk is not None and not hasattr(instance, '_previously_removed'):
             update_counter(parent_model, parent_pk, counter_name, -1)
 
 
@@ -87,38 +87,48 @@ def post_delete_receiver(sender, instance, origin, **kwargs):
 
 def connect_counters(*models):
     """
-    Register counter fields and connect post_save & post_delete signal handlers for the affected models.
+    Register counter fields and connect signal handlers for their child models.
+    Ensures exactly one receiver per child (sender), even when multiple counters
+    reference the same sender (e.g., Device).
     """
-    for model in models:
+    connected = set()  # child models we've already connected
 
+    for model in models:
         # Find all CounterCacheFields on the model
-        counter_fields = [
-            field for field in model._meta.get_fields() if type(field) is CounterCacheField
-        ]
+        counter_fields = [field for field in model._meta.get_fields() if isinstance(field, CounterCacheField)]
 
         for field in counter_fields:
             to_model = apps.get_model(field.to_model_name)
 
             # Register the counter in the registry
             change_tracking_fields = registry['counter_fields'][to_model]
-            change_tracking_fields[f"{field.to_field_name}_id"] = field.name
+            change_tracking_fields[f'{field.to_field_name}_id'] = field.name
+
+            # Connect signals once per child model
+            if to_model in connected:
+                continue
+
+            # Ensure dispatch_uid is unique per model (sender), not per field
+            uid_base = f'countercache.{to_model._meta.label_lower}'
 
             # Connect the post_save and post_delete handlers
             post_save.connect(
                 post_save_receiver,
                 sender=to_model,
                 weak=False,
-                dispatch_uid=f'{model._meta.label}.{field.name}'
+                dispatch_uid=f'{uid_base}.post_save',
             )
             pre_delete.connect(
                 pre_delete_receiver,
                 sender=to_model,
                 weak=False,
-                dispatch_uid=f'{model._meta.label}.{field.name}'
+                dispatch_uid=f'{uid_base}.pre_delete',
             )
             post_delete.connect(
                 post_delete_receiver,
                 sender=to_model,
                 weak=False,
-                dispatch_uid=f'{model._meta.label}.{field.name}'
+                dispatch_uid=f'{uid_base}.post_delete',
             )
+
+            connected.add(to_model)