fix(deps): bump langgraph-checkpoint to >=4.0.0 to fix RCE deserialization CVE

[raphael-intugle]

Summary

• Adds explicit langgraph-checkpoint>=4.0.0 constraint in pyproject.toml to resolve Dependabot alert added fmcg snowflake notebook #50
• uv.lock updated: langgraph-checkpoint bumped from 3.0.1 → 4.0.1

Vulnerability

LangGraph: BaseCache Deserialization of Untrusted Data may lead to Remote Code Execution

• Affected: langgraph-checkpoint < 4.0.0
• Patched: 4.0.0
• Severity: Moderate