fix: add missing imports in test code

- Add ProxyError import and fix Result type annotation in tls.rs
- Add Arc import in stats/mod.rs test module
- Add BodyExt import in metrics.rs test module

These imports were missing causing compilation failures in
cargo test --release with 10 errors.

src/protocol/tls.rs

@@ -7,6 +7,7 @@
 #![allow(dead_code)]
 
 use crate::crypto::{sha256_hmac, SecureRandom};
+use crate::error::ProxyError;
 use super::constants::*;
 use std::time::{SystemTime, UNIX_EPOCH};
 use num_bigint::BigUint;
@@ -614,7 +615,7 @@ pub fn parse_tls_record_header(header: &[u8; 5]) -> Option<(u8, u16)> {
 ///
 /// This is useful for testing that our ServerHello is well-formed.
 #[cfg(test)]
-fn validate_server_hello_structure(data: &[u8]) -> Result<()> {
+fn validate_server_hello_structure(data: &[u8]) -> Result<(), ProxyError> {
     if data.len() < 5 {
         return Err(ProxyError::InvalidTlsRecord {
             record_type: 0,