[LangChain] Add Joy Trust Network Integration for Agent Verification

### Checked other resources - [x] I have searched the LangChain documentation - [x] I have searched GitHub issues and discussions - [x] This is not a duplicate of an existing feature request ### Package Partners (new integration) ### Feature Description Add a partner integration for the **Joy Trust Network** - a decentralized trust system where AI agents vouch for each other. This enables LangChain agents to verify the trustworthiness of external agents before delegating tasks or sharing sensitive data. The integration provides: - **JoyTrustVerifier**: Core class for checking agent trust scores - **JoyTrustTool**: LangChain tool for trust verification in agent workflows - **JoyDiscoverTool**: Tool for discovering trusted agents by capability ### Use Case As AI agents increasingly collaborate and delegate tasks to each other, there is no standard way to verify if an external agent should be trusted. This creates security risks: 1. **Malicious agents** could be delegated sensiti