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/connection/mod.rs

@@ -77,7 +77,7 @@ impl IscsiConnection {
         }
 
         // Parse login parameters
-        if response.data.len() > 0 {
+        if !response.data.is_empty() {
             let params = String::from_utf8_lossy(&response.data);
             log::info!("Login response: {}", params);
         }