chore(prebuilt): Remove dead code from prebuilt tests (#5555)

Fixes #5554

This PR removes unused utility classes and functions from the prebuilt
tests directory to clean up dead code.

Changes include:
- Removed unused classes from `libs/prebuilt/tests/any_str.py`:
  - Deleted FloatBetween, AnyDict, AnyVersion, and UnsortedSequence
  - Kept only AnyStr class

- Removed unused functions from `libs/prebuilt/tests/messages.py`:
  - Deleted _AnyIdDocument and _AnyIdAIMessageChunk
  - Kept _AnyIdHumanMessage and _AnyIdToolMessage

- Removed unused classes from `libs/prebuilt/tests/memory_assert.py`:
- Deleted NoopSerializer, MemorySaverAssertCheckpointMetadata, and
MemorySaverNoPending
  - Kept MemorySaverAssertImmutable

Verification:
- Manually checked for no remaining references to removed code
- Maintained existing import structures
- Preserved functionality of the prebuilt test suite

The changes reduce code complexity and remove unnecessary utility
classes that were not being used in the test suite.

---------

Co-authored-by: open-swe-dev[bot] <open-swe-dev@users.noreply.github.com>
Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/prebuilt/tests/memory_assert.py

@@ -1,31 +1,19 @@
-import asyncio
 import os
 import tempfile
 from collections import defaultdict
 from functools import partial
-from typing import Any, Optional
-
-from langchain_core.runnables import RunnableConfig
+from typing import Optional
 
 from langgraph.checkpoint.base import (
     ChannelVersions,
     Checkpoint,
     CheckpointMetadata,
-    CheckpointTuple,
     SerializerProtocol,
 )
 from langgraph.checkpoint.memory import InMemorySaver, PersistentDict
 from langgraph.pregel.checkpoint import copy_checkpoint
 
 
-class NoopSerializer(SerializerProtocol):
-    def loads_typed(self, data: tuple[str, bytes]) -> Any:
-        return data[1]
-
-    def dumps_typed(self, obj: Any) -> tuple[str, bytes]:
-        return "type", obj
-
-
 class MemorySaverAssertImmutable(InMemorySaver):
     storage_for_copies: defaultdict[str, dict[str, dict[str, Checkpoint]]]
 
@@ -69,66 +57,3 @@ class MemorySaverAssertImmutable(InMemorySaver):
         )
         # call super to write checkpoint
         return super().put(config, checkpoint, metadata, new_versions)
-
-
-class MemorySaverAssertCheckpointMetadata(InMemorySaver):
-    """This custom checkpointer is for verifying that a run's configurable
-    fields are merged with the previous checkpoint config for each step in
-    the run. This is the desired behavior. Because the checkpointer's (a)put()
-    method is called for each step, the implementation of this checkpointer
-    should produce a side effect that can be asserted.
-    """
-
-    def put(
-        self,
-        config: RunnableConfig,
-        checkpoint: Checkpoint,
-        metadata: CheckpointMetadata,
-        new_versions: ChannelVersions,
-    ) -> None:
-        """The implementation of put() merges config["configurable"] (a run's
-        configurable fields) with the metadata field. The state of the
-        checkpoint metadata can be asserted to confirm that the run's
-        configurable fields were merged with the previous checkpoint config.
-        """
-        configurable = config["configurable"].copy()
-
-        # remove checkpoint_id to make testing simpler
-        checkpoint_id = configurable.pop("checkpoint_id", None)
-        thread_id = config["configurable"]["thread_id"]
-        checkpoint_ns = config["configurable"]["checkpoint_ns"]
-        self.storage[thread_id][checkpoint_ns].update(
-            {
-                checkpoint["id"]: (
-                    self.serde.dumps_typed(checkpoint),
-                    # merge configurable fields and metadata
-                    self.serde.dumps_typed({**configurable, **metadata}),
-                    checkpoint_id,
-                )
-            }
-        )
-        return {
-            "configurable": {
-                "thread_id": config["configurable"]["thread_id"],
-                "checkpoint_id": checkpoint["id"],
-            }
-        }
-
-    async def aput(
-        self,
-        config: RunnableConfig,
-        checkpoint: Checkpoint,
-        metadata: CheckpointMetadata,
-        new_versions: ChannelVersions,
-    ) -> RunnableConfig:
-        return await asyncio.get_running_loop().run_in_executor(
-            None, self.put, config, checkpoint, metadata, new_versions
-        )
-
-
-class MemorySaverNoPending(InMemorySaver):
-    def get_tuple(self, config: RunnableConfig) -> Optional[CheckpointTuple]:
-        result = super().get_tuple(config)
-        if result:
-            return CheckpointTuple(result.config, result.checkpoint, result.metadata)
-        return result