fix: resolve clippy warnings and test errors

- Implement FromStr trait for NodeType instead of custom from_str method
- Fix redundant_closure warning in server.rs:455
- Add #[allow(clippy::too_many_arguments)] for new_file_node
- Fix unused variables in tests (_user_id, _conn)
- Remove unused imports (NodeType, serde_json::json)
- Replace len() > 0 with !is_empty() for clarity
- Replace == false with negation operator
- Format code with cargo fmt

tests/convert_test.rs

@@ -54,7 +54,7 @@ fn test_is_apple_format_ext() {
 fn test_is_document_ext_case_insensitive() {
     //測試小寫（convert.rs使用小寫比較）
     assert!(is_document_ext("docx"));
-    assert!(is_document_ext("DOCX") == false); //函數未轉小寫，直接比較
+    assert!(!is_document_ext("DOCX")); //函數未轉小寫，直接比較
 }
 
 #[test]