Bump langgraph from 0.2.73 to 0.6.3

Bumps [langgraph](https://github.com/langchain-ai/langgraph) from 0.2.73 to 0.6.3.
- [Release notes](https://github.com/langchain-ai/langgraph/releases)
- [Commits](langchain-ai/langgraph@0.2.73...0.6.3)

---
updated-dependencies:
- dependency-name: langgraph
  dependency-version: 0.6.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]