Get the namespace of the LangChain object.
The default implementation splits cls.__module__ on '.', e.g.
langchain_openai.chat_models becomes
["langchain_openai", "chat_models"]. This value is used by lc_id to
build the serialization identifier.
New partner packages should not override this method. The default
behavior is correct for any class whose module path already reflects
its package name. Some older packages (e.g. langchain-openai,
langchain-anthropic) override it to return a legacy-style namespace
like ["langchain", "chat_models", "openai"], matching the module
paths that existed before those integrations were split out of the
main langchain package. Those overrides are kept for
backwards-compatible deserialization; new packages should not copy them.
Deserialization mapping is handled separately by
SERIALIZABLE_MAPPING in langchain_core.load.mapping.
