feat: add yjs-libp2p collaborative editing example

[NiKrause]

Description

This PR adds a new example demonstrating real-time collaborative editing using Yjs and libp2p. The example showcases how to create a custom Yjs connection provider using libp2p instead of the standard y-webrtc connector.

What's Included

• Complete working example: A collaborative text editor with real-time synchronization
• Custom Yjs Provider: Libp2p-based connection provider implementing the Yjs provider interface
• Relay Server: Standalone relay node for NAT traversal and peer discovery
• Comprehensive Tests: Playwright tests with automated setup/teardown
• CI Integration: Added to GitHub Actions workflow with build steps
• Documentation: Detailed README explaining architecture, setup, and usage

Key Features Demonstrated

• WebRTC Support: Direct peer-to-peer connections for low-latency sync
• Circuit Relay: NAT traversal via relay servers
• DCUTR: Direct Connection Upgrade through Relay (hole punching)
• AutoNAT: Automatic NAT detection
• GossipSub: PubSub-based document synchronization
• Peer Discovery: Automatic connection to peers on the same topic
• State Synchronization: Uses Yjs's state vector protocol for efficient syncing

Architecture

The example consists of:

1. Browser clients that run libp2p nodes with WebRTC and Circuit Relay
2. A relay server for bootstrapping connections and NAT traversal
3. A custom Libp2pProvider that integrates Yjs with libp2p's pubsub

CI Improvements

• Added build step to CI workflow for examples with build scripts
• Conditional build logic to avoid errors for examples without build steps

Testing

The example includes comprehensive Playwright tests that:

• Automatically start and stop the relay server
• Test real-time synchronization between multiple browser instances
• Verify peer discovery and connection establishment

Notes & open questions

The example provides a practical demonstration of:

• Building custom Yjs providers for alternative transport layers
• Configuring libp2p for browser-to-browser communication
• Implementing NAT traversal strategies (relay + DCUTR)
• Integrating CRDTs with decentralized networking

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works