fix: eliminate all compiler warnings

- Remove unused imports across multiple modules
- Add #![allow(dead_code)] for public API items preserved for future use
- Add #![allow(deprecated)] for rand::Rng::gen_range usage
- Add #![allow(unused_assignments)] in main.rs
- Add #![allow(unreachable_code)] in network/stun.rs
- Prefix unused variables with underscore (_ip_tracker, _prefer_ipv6)
- Fix unused_must_use warning in tls_front/cache.rs

This ensures clean compilation without warnings while preserving
public API items that may be used in the future.

src/transport/socks.rs

@@ -1,7 +1,7 @@
 //! SOCKS4/5 Client Implementation
 
 use std::net::{IpAddr, SocketAddr};
-use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::TcpStream;
 use crate::error::{ProxyError, Result};