fix: correct iot_class to local_push

Coordinator prefers CoAP OBSERVE push notifications (observe.py) over
polling when the device supports it, falling back to polling only when
observe mode isn't available or drops.

custom_components/localthings/manifest.json

@@ -5,7 +5,7 @@
   "config_flow": true,
   "dependencies": [],
   "documentation": "https://github.com/mbillow/localthings",
-  "iot_class": "local_polling",
+  "iot_class": "local_push",
   "issue_tracker": "https://github.com/mbillow/localthings/issues",
   "requirements": [
     "cbor2>=5.4.6",