Check the registry entry in sensor unit_of_measurement instead of unique_id (#96731)

The unit_of_measurement check was checking to see if the entity has
a unique_id instead of a registry entry. Its much cheaper to check
for the registry_entry than the unique id since some entity have
to construct it every time its read

homeassistant/components/sensor/__init__.py

@@ -453,7 +453,7 @@ class SensorEntity(Entity):
             return self._sensor_option_unit_of_measurement
 
         # Second priority, for non registered entities: unit suggested by integration
-        if not self.unique_id and (
+        if not self.registry_entry and (
             suggested_unit_of_measurement := self.suggested_unit_of_measurement
         ):
             return suggested_unit_of_measurement