A: Code quality improvements - fix clippy warnings

- Remove unused imports in server.rs (Body, HeaderValue, RwLock)
- Remove unused imports in forward_acl.rs (tests still need Ipv4Addr)
- Remove unused imports in host_key.rs (Read, Write)
- Remove unused imports in kex_exchange.rs (HostKeyType)
- Remove unused imports in known_hosts.rs (tests need Ipv4Addr)
- Remove unused imports in multiplex.rs (Arc)
- Auto-fix other unused imports via clippy --fix

Tests: 303 passed, 0 failed (4 new tests added)

markbase-core/src/s3.rs

@@ -733,15 +733,12 @@ pub async fn complete_multipart_upload(
     let mut final_size: u64 = 0;
 
     for part in &upload.parts {
-        let part_file_path = temp_dir.join(format!("s3_multipart_{}_{}_*.tmp", upload_id, part.part_number));
+        let _part_file_path = temp_dir.join(format!("s3_multipart_{}_{}_*.tmp", upload_id, part.part_number));
         
         // Find the actual part file (with UUID suffix)
-        let part_files: Option<Vec<_>> = std::fs::read_dir(&temp_dir).ok()
-            .and_then(|dir| {
-                Some(dir.filter_map(|e| e.ok())
+        let part_files: Option<Vec<_>> = std::fs::read_dir(&temp_dir).ok().map(|dir| dir.filter_map(|e| e.ok())
                     .filter(|e| e.file_name().to_str().unwrap_or("").starts_with(&format!("s3_multipart_{}_{}_", upload_id, part.part_number)))
-                    .collect::<Vec<_>>())
-            });
+                    .collect::<Vec<_>>());
 
         if let Some(files) = part_files {
             if let Some(part_file_entry) = files.first() {