feat: Implement Rendezvous module in py-libp2p

[sumanjeet0012]

What was wrong?

The py-libp2p library lacked a Rendezvous protocol implementation for peer discovery. This missing functionality created a gap between py-libp2p and other libp2p implementations (Go, Rust) that already support rendezvous-based peer discovery through namespaces.

How was it fixed?

1. Core Module Implementation

• libp2p/discovery/rendezvous/ directory with complete protocol implementation:
  • service.py: Rendezvous service handling peer registrations and discovery
  • client.py: Low-level protocol client
  • discovery.py: High-level discovery interface with caching and auto-refresh
  • config.py: Configuration constants and defaults
  • errors.py: Protocol-specific exception classes
  • messages.py: Protocol buffer message utilities

2. Key Features

• Peer Registration: Advertise peers under namespaces with configurable TTL
• Peer Discovery: Find peers by namespace with pagination support
• Auto-refresh: Optional automatic re-registration before TTL expiry
• Caching: Discovery result caching to reduce repeated queries
• Resource Management: TTL-based cleanup and connection management
• Error Handling: Comprehensive error types and status codes

3. Protocol Compliance

• Full libp2p rendezvous protocol specification compliance
• Protocol buffer message serialization/deserialization
• Pagination support with limit and cookie-based navigation
• Proper error status handling and propagation

4. Examples and Integration

• Complete example demonstrating server and client usage
• Command-line interface for testing (--mode server/client)
• Optional refresh functionality showcase
• Seamless integration with existing py-libp2p host implementation

Benefits

• Feature Parity: Brings py-libp2p closer to other libp2p implementations
• Flexible Discovery: Application-specific peer discovery patterns
• Bootstrap Alternative: Lightweight alternative to DHT-based discovery
• Namespace Organization: Logical grouping of peers by service type

To-Do

• Clean up commit history
• Add documentation updates
• Add entry to release notes