Add some docs to OriginalWeightsStorage and fix type hints.

invokeai/backend/util/original_weights_storage.py

@@ -8,9 +8,13 @@ from invokeai.backend.util.devices import TorchDevice
 
 
 class OriginalWeightsStorage:
+    """A class for tracking the original weights of a model for patch/unpatch operations."""
+
     def __init__(self, cached_weights: Optional[Dict[str, torch.Tensor]] = None):
-        self._weights = {}
-        self._changed_weights = set()
+        # The original weights of the model.
+        self._weights: dict[str, torch.Tensor] = {}
+        # The keys of the weights that have been changed (via `save()`) during the lifetime of this instance.
+        self._changed_weights: set[str] = set()
         if cached_weights:
             self._weights.update(cached_weights)