Updates base persister load docs

So that they describe the expected behavior better.

burr/core/persistence.py

@@ -32,9 +32,10 @@ def load(
         :param partition_key: the partition key. Note this could be None, but it's up to the persistor to whether
             that is a valid value it can handle.
         :param app_id: the identifier for the app instance being recorded.
-        :param sequence_id: optional, the state corresponding to a specific point in time.
-            If not provided, should return the latest.
-        :return: position, state, sequence_id
+        :param sequence_id: optional, the state corresponding to a specific point in time. Specifically state at the
+            end of the action with this sequence_id. If sequence_id is not provided, persistor should return the state
+            from the latest fully completed action.
+        :return: PersistedStateData or None
         """
         pass
 

burr/tracking/client.py

@@ -621,15 +621,15 @@ def load(
         for key in to_delete:
             del prior_state[key]
         prior_state["__SEQUENCE_ID"] = sequence_id  # add the sequence id back
-        return {
-            "partition_key": partition_key,
-            "app_id": app_id,
-            "sequence_id": sequence_id,
-            "position": position,
-            "state": State.deserialize(prior_state, **self.serde_kwargs),
-            "created_at": datetime.datetime.fromtimestamp(os.path.getctime(path)).isoformat(),
-            "status": "completed" if line["exception"] is None else "failed",
-        }
+        return PersistedStateData(
+            partition_key=partition_key,
+            app_id=app_id,
+            sequence_id=sequence_id,
+            position=position,
+            state=State.deserialize(prior_state, **self.serde_kwargs),
+            created_at=datetime.datetime.fromtimestamp(os.path.getctime(path)).isoformat(),
+            status="completed" if line["exception"] is None else "failed",
+        )
 
 
 # TODO -- implement async version