langchain-ai/langchain langchain==1.4.0

Changes since langchain==1.3.18 docs(langchain): runnable `langchain.mcp` examples (#39976) feat(langchain): `langchain.mcp` namespace, `MCPAdapter` (#39939) perf(anthropic,langchain): omit middleware trace inputs (#40098) fix(langchain): include model destination in agent tool routing (#38355) chore(langchain): bump vcrpy test dependency minimum to `>=8.2.0` (#39942)