Build LangChain Tool: NEAR Event Listener

Description

## Overview
Create a LangChain tool that monitors NEAR blockchain events and triggers agent actions based on on-chain activity.

## Why This Matters
Reactive agents need to respond to blockchain events. This tool enables event-driven agent architectures.

## Technical Requirements
- Subscribe to account events
- Filter by event type
- Parse event data
- Trigger callbacks
- Handle reconnection

## Deliverables
1. PyPI package
2. Event subscription API
3. Filtering capabilities
4. Reliable reconnection