Restore august lock changed_by state on restart (#32340)

* Various code review items from previous PRs

* Add a test for fetching the doorbell camera image

* Switch to using UNIT_PERCENTAGE for battery charge unit

* Add tests for changed_by

homeassistant/components/august/sensor.py

@@ -2,6 +2,7 @@
 import logging
 
 from homeassistant.components.sensor import DEVICE_CLASS_BATTERY
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.core import callback
 from homeassistant.helpers.entity import Entity
 
@@ -111,7 +112,7 @@ class AugustBatterySensor(AugustEntityMixin, Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement."""
-        return "%"  # UNIT_PERCENTAGE will be available after PR#32094
+        return UNIT_PERCENTAGE
 
     @property
     def device_class(self):