refactor: make better use of HASS sensor base class

- Don't re-implement sensor property methods unless it's really
  necessary. Instead, implement the values that the existing property
  methods depend on.
- Fix automatic temperature conversions not working

custom_components/hubitat/device.py

@@ -90,6 +90,13 @@ def get_attr(self, attr: str) -> float | int | str | None:
             return self._device.attributes[attr].value
         return None
 
+    @callback
+    def get_attr_unit(self, attr: str) -> str | None:
+        """Get the unit of an attribute."""
+        if attr in self._device.attributes:
+            return self._device.attributes[attr].unit
+        return None
+
     @callback
     def get_float_attr(self, attr: str) -> float | None:
         """Get the current value of an attribute."""

custom_components/hubitat/hubitatmaker/types.py

@@ -25,12 +25,13 @@ def values(self) -> list[str] | None:
             return None
         return self._properties["values"]
 
-    def update_value(self, value: str | float) -> None:
+    def update_value(self, value: str | float, unit: str | None = None) -> None:
         self._properties["currentValue"] = value
+        self._properties["unit"] = unit
 
     @property
-    def unit(self) -> str:
-        return self._properties["unit"]
+    def unit(self) -> str | None:
+        return self._properties.get("unit")
 
     def __iter__(self):
         for key in "name", "type", "value", "unit":
@@ -98,7 +99,7 @@ def update_attr(
         self, attr_name: str, value: str | int, value_unit: str | None
     ) -> None:
         attr = self.attributes[attr_name]
-        attr.update_value(value)
+        attr.update_value(value, value_unit)
         self._last_update = time()
 
     def update_state(self, properties: dict[str, Any]) -> None: