Add user agent

lib/services/runtime_details_service.dart

@@ -0,0 +1,24 @@
+import 'dart:io';
+
+import 'package:hiddify/utils/utils.dart';
+import 'package:package_info_plus/package_info_plus.dart';
+
+class RuntimeDetailsService with InfraLogger {
+  late final PackageInfo _packageInfo;
+
+  String get appVersion => _packageInfo.version;
+  String get buildNumber => _packageInfo.buildNumber;
+
+  late final String operatingSystem = Platform.operatingSystem;
+  late final String userAgent;
+
+  Future<void> init() async {
+    loggy.debug("initializing");
+    _packageInfo = await PackageInfo.fromPlatform();
+    userAgent = "HiddifyNext/$appVersion ($operatingSystem)";
+
+    loggy.info(
+      "os: [$operatingSystem](${Platform.operatingSystemVersion}), processor count [${Platform.numberOfProcessors}]",
+    );
+  }
+}