langchain

cea379e7 - community, core[callbacks]: move FileCallbackHandler from community to core (#20495)

community, core[callbacks]: move FileCallbackHandler from community to core (#20495) **Description:** Move `FileCallbackHandler` from community to core **Issue:** #20493 **Dependencies:** None (imo) `FileCallbackHandler` is a built-in LangChain callback handler like `StdOutCallbackHandler` and should properly be in in core.