Produce "checkpoint" events for stream_mode=debug.
map_debug_checkpoint(
config: RunnableConfig,
channels: Mapping[str, BaseChannel],
stream_channels: str | Sequence[str],
metadata: CheckpointMetadata,
tasks: Iterable[PregelExecutableTask],
pending_writes: list[PendingWrite],
parent_config: RunnableConfig | None,
output_keys: str | Sequence[str]
) -> Iterator[CheckpointPayload]