build(deps): bump langchain (#4579)

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.3.21 to 0.3.30.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](https://github.com/langchain-ai/langchain/compare/langchain==0.3.21...langchain==0.3.30)

---
updated-dependencies:
- dependency-name: langchain
  dependency-version: 0.3.30
  dependency-type: direct:production
...

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