chore: apply format/lint fixes across checkpoint, checkpoint-postgres, prebuilt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

libs/checkpoint/langgraph/checkpoint/base/__init__.py

@@ -36,7 +36,9 @@ class DeltaValue:
     """Returned by DeltaChannel.checkpoint(). Represents one step's writes."""
 
     delta: list[Any]
-    prev_checkpoint_id: str | None  # ID of checkpoint containing previous blob; None = chain root
+    prev_checkpoint_id: (
+        str | None
+    )  # ID of checkpoint containing previous blob; None = chain root
 
 
 @dataclasses.dataclass

libs/checkpoint/tests/test_jsonplus.py

@@ -1004,7 +1004,9 @@ def test_delta_value_serde_round_trip() -> None:
     from langgraph.checkpoint.serde.jsonplus import JsonPlusSerializer
 
     serde = JsonPlusSerializer()
-    original = DeltaValue(delta=[{"type": "human", "content": "hi"}], prev_checkpoint_id="abc-123")
+    original = DeltaValue(
+        delta=[{"type": "human", "content": "hi"}], prev_checkpoint_id="abc-123"
+    )
     type_tag, blob = serde.dumps_typed(original)
     assert type_tag == "diff"
     loaded = serde.loads_typed((type_tag, blob))