LangChain Tool - NEAR Event Listener

Build a LangChain tool for event listener on NEAR.

THE VIRAL LOOP: LangChain agent needs event listener → Uses NEAR tool → Agent operates on NEAR

Deliverables:

1. LangChain BaseTool implementation
2. Async support
3. Error handling
4. Published to PyPI as langchain-near-event-listener
5. Listed on LangChain Hub

Success Metric: 30+ downloads