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/middle_proxy/mod.rs

@@ -17,8 +17,10 @@ mod wire;
 use bytes::Bytes;
 
 pub use health::me_health_monitor;
+#[allow(unused_imports)]
 pub use ping::{run_me_ping, format_sample_line, MePingReport, MePingSample, MePingFamily};
 pub use pool::MePool;
+#[allow(unused_imports)]
 pub use pool_nat::{stun_probe, detect_public_ip};
 pub use registry::ConnRegistry;
 pub use secret::fetch_proxy_secret;