Refactor proxy and transport modules for improved safety and performance

- Enhanced linting rules in `src/proxy/mod.rs` to enforce stricter code quality checks in production.
- Updated hash functions in `src/proxy/middle_relay.rs` for better efficiency.
- Added new security tests in `src/proxy/tests/middle_relay_stub_completion_security_tests.rs` to validate desynchronization behavior.
- Removed ignored test stubs in `src/proxy/tests/middle_relay_security_tests.rs` to clean up the test suite.
- Improved error handling and code readability in various transport modules, including `src/transport/middle_proxy/config_updater.rs` and `src/transport/middle_proxy/pool.rs`.
- Introduced new padding functions in `src/stream/frame_stream_padding_security_tests.rs` to ensure consistent behavior across different implementations.
- Adjusted TLS stream validation in `src/stream/tls_stream.rs` for better boundary checking.
- General code cleanup and dead code elimination across multiple files to enhance maintainability.

src/stream/frame_codec.rs

@@ -652,7 +652,7 @@ mod tests {
             let mut out = BytesMut::new();
             codec.encode(&frame, &mut out).unwrap();
 
-            assert!(out.len() >= 4 + payload.len() + 1);
+            assert!(out.len() > 4 + payload.len());
             let wire_len = u32::from_le_bytes([out[0], out[1], out[2], out[3]]) as usize;
             assert!(
                 (payload.len() + 1..=payload.len() + 3).contains(&wire_len),