Various type hint improvements (#37952)

homeassistant/helpers/area_registry.py

@@ -2,7 +2,7 @@
 from asyncio import Event
 from collections import OrderedDict
 import logging
-from typing import Iterable, MutableMapping, Optional, cast
+from typing import Dict, Iterable, List, MutableMapping, Optional, cast
 import uuid
 
 import attr
@@ -132,7 +132,7 @@ class AreaRegistry:
         self._store.async_delay_save(self._data_to_save, SAVE_DELAY)
 
     @callback
-    def _data_to_save(self) -> dict:
+    def _data_to_save(self) -> Dict[str, List[Dict[str, Optional[str]]]]:
         """Return data of area registry to store in a file."""
         data = {}