Update langchain

[TristanLecourtois]

Purpose

• Ensure compatibility with the latest version of LangChain.
• Fix a bug in ros2_topic_list, ros2_service_list and ros2_node_list where the pattern parameter was not typed as optional, which caused a test failure.

Proposed Changes

• [CHANGE] Updated LangChain version in the project dependencies.
• [FIX] Modified ros2_topic_list to correctly type pattern as Optional[str] instead of str.
• [FIX] Updated the related test

Issues

• Related to internal compatibility issues with updated LangChain versions.
• No external GitHub issue linked.

Testing

• Ran pytest on all test files.
• All tests passed or skipped correctly.

[RobRoyce]

Thank you @TristanLecourtois. This should resolve #61. I'll merge in after running workflows.