Fix code quality: trailing whitespace, unused imports, clippy warnings

- Fix trailing whitespace in kex.rs and s3.rs
- Add missing KexProposal import in kex_complete.rs
- Auto-fix clippy warnings across all crates
- All 153 tests pass

rust-iscsi-initiator/src/discovery/mod.rs

@@ -33,7 +33,7 @@ impl Discovery {
             let response = conn.recv_pdu().await?;
 
             // Parse SendTargets response
-            if response.data.len() > 0 {
+            if !response.data.is_empty() {
                 let targets_str = String::from_utf8_lossy(&response.data);
                 let targets = targets_str
                     .lines()