chore(deps): bump langgraph-checkpoint from 3.0.1 to 4.0.0

Bumps [langgraph-checkpoint](https://github.com/langchain-ai/langgraph) from 3.0.1 to 4.0.0.
- [Release notes](https://github.com/langchain-ai/langgraph/releases)
- [Commits](langchain-ai/langgraph@checkpoint==3.0.1...checkpoint==4.0.0)

---
updated-dependencies:
- dependency-name: langgraph-checkpoint
  dependency-version: 4.0.0
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]