Add long-term statistics for Guardian sensors (#55413)

* Add long-term statistics for Guardian sensors

* Code review

homeassistant/components/guardian/sensor.py

@@ -1,7 +1,11 @@
 """Sensors for the Elexa Guardian integration."""
 from __future__ import annotations
 
-from homeassistant.components.sensor import SensorEntity, SensorEntityDescription
+from homeassistant.components.sensor import (
+    STATE_CLASS_MEASUREMENT,
+    SensorEntity,
+    SensorEntityDescription,
+)
 from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import (
     DEVICE_CLASS_BATTERY,
@@ -41,6 +45,7 @@ SENSOR_DESCRIPTION_TEMPERATURE = SensorEntityDescription(
     name="Temperature",
     device_class=DEVICE_CLASS_TEMPERATURE,
     native_unit_of_measurement=TEMP_FAHRENHEIT,
+    state_class=STATE_CLASS_MEASUREMENT,
 )
 SENSOR_DESCRIPTION_UPTIME = SensorEntityDescription(
     key=SENSOR_KIND_UPTIME,