feat(p2p): add layer allocation logging in heartbeat

[JasonOE]

Summary

This PR adds layer allocation information logging to the worker heartbeat mechanism. Workers now receive and log their assigned layer ranges (start_layer, end_layer) and model name during each heartbeat.

Changes

Scheduler Side (rpc_connection_handler.py)

• Modified node_update() RPC method to return layer allocation information
• Returns {node_id, model_name, start_layer, end_layer} in the response

Worker Side (p2p/server.py)

• Updated heartbeat announcer thread to capture and log layer allocation from scheduler response
• Added info-level logging: Heartbeat: Node {peer_id}... Model: {model_name}, Layers: [{start}, {end})
• Helps with debugging and monitoring node layer assignments

Benefits

• Better observability: Workers can now see their assigned layers in logs
• Debugging aid: Easier to troubleshoot layer allocation issues
• Real-time monitoring: Layer assignments are visible in heartbeat logs every 10 seconds

Testing

• Code compiles without errors
• Commit message follows conventional commits format
• Manual testing of heartbeat logging (pending)

Related Issues