feat: add XML and HTML formatting support (#721)

lib/utils/xml_formatter.dart

@@ -0,0 +1,18 @@
+import 'package:xml/xml.dart';
+
+class XML {
+  /// 格式化 XML
+  static String pretty(String xmlString) {
+    if (xmlString.trim().isEmpty || !xmlString.contains('<')) {
+      return xmlString;
+    }
+
+    try {
+      final document = XmlDocument.parse(xmlString);
+      return document.toXmlString(pretty: true, indent: '  ');
+    } catch (_) {
+      return xmlString;
+    }
+  }
+}
+