fix: add warning log for missing skip_push_update_on_save

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MichaelUray

openwisp_controller/config/controller/views.py

@@ -482,6 +482,12 @@ def _update_device_name(self, request, device):
             skip = getattr(device, "skip_push_update_on_save", None)
             if callable(skip):
                 skip()
+            else:
+                logger.warning(
+                    "Device %s does not implement skip_push_update_on_save(); "
+                    "continuing registration without push-skip optimization.",
+                    device.pk,
+                )
 
 
 class GetVpnView(SingleObjectMixin, View):