Make iot time timezone aware (#1147)

Also makes on_since for iot devices use device time.
Changes the return value for device.timezone to be tzinfo instead of a dict.

kasa/iot/modules/lightpreset.py

@@ -41,7 +41,7 @@ class LightPreset(IotModule, LightPresetInterface):
     _presets: dict[str, IotLightPreset]
     _preset_list: list[str]
 
-    def _post_update_hook(self):
+    async def _post_update_hook(self):
         """Update the internal presets."""
         self._presets = {
             f"Light preset {index+1}": IotLightPreset(**vals)