refactor: remove unused cast import in base.py

Author: 5enxia

libs/langgraph-checkpoint-aws/langgraph_checkpoint_aws/store/dynamodb/base.py

@@ -12,7 +12,7 @@
 from collections.abc import Iterable, Iterator
 from contextlib import contextmanager
 from datetime import datetime, timezone
-from typing import Any, cast
+from typing import Any
 
 import boto3
 import orjson