chore: Add comment about firmware updates

Author: allenporter

roborock/devices/traits/v1/device_features.py

@@ -21,7 +21,8 @@ async def refresh(self) -> Self:
         """Refresh the contents of this trait.
 
         This will use cached device features if available since they do not
-        change often and this avoids unnecessary RPC calls.
+        change often and this avoids unnecessary RPC calls. This would only
+        ever change with a firmware update, so caching is appropriate.
         """
         cache_data = await self._cache.get()
         if cache_data.device_features is not None: