Fix type of rooms_dict property (#66)

The `_rooms_dict` member is a nested dictionary keyed by mac ID, then room ID, but the `rooms_dict` property that wraps it claims to return a type of `dict[str, LyricRoom]`. This corrects the type signature.

aiolyric/__init__.py

@@ -48,7 +48,7 @@ def locations_dict(self) -> dict:
         return self._locations_dict
 
     @property
-    def rooms_dict(self) -> dict[str, LyricRoom]:
+    def rooms_dict(self) -> dict[str, dict[str, LyricRoom]]:
         return self._rooms_dict
 
     async def get_devices(