Announcing LangChain v0.3

LangChain v0.3 has been released for both Python and Javascript ecosystems. For the Python version, all packages have been upgraded from Pydantic 1 to Pydantic 2, with support for Pydantic 1 ending in June 2024. Additionally, Python 3.8 will no longer be supported as its end-of-life is October 2024. For the Javascript version, LangChain packages now have @langchain/core as a peer dependency instead of a direct one, and callbacks are now backgrounded and non-blocking by default. Other improvements include moving more integrations to their own langchain-{name} packages, revamping integration docs and API references, simplifying tool definition and usage, adding utilities for chat models, and adding the ability to dispatch custom events. LangGraph is now recommended for building agents with LLMs.