Refactor network layer, P2P handler, and update dependencies

[Banyc]

Summary

Network Layer

• Split Connection trait into ConnRead + ConnWrite + HasPeerAddr for future ownership split
• Combined stun_ip + stun_port fields into StunAddr type
• Replaced crate::Result with anyhow::Result throughout

P2P Handler

• Removed Arc<RwLock<>> wrapping from PeerHandler, simplified to channel-based API
• Restructured peer state into PeerSet with cleaner address tracking via LastActive wrapper
• Simplified peer address storage: replaced separate ipv6/port with Option<SocketAddr>

Server

• Flattened nested tokio::select! in server handler
• Updated configuration watcher for notify 8.0 API

Dependencies

• Replaced blocking ureq HTTP client with async reqwest
• Upgraded axum 0.7 → 0.8, notify 7 → 8
• Updated to Rust edition 2024 with inline format args
• Bumped various crate versions

Internal

• Moved binaries to src/bin/
• Minor code cleanup and formatting fixes