feat(android): 添加 CH934X USB 转串口芯片支持

- 在 AndroidManifest.xml 中添加 USB Host 权限声明
- 集成 CH934X Android SDK 并通过反射调用原生功能
- 实现设备查找、串口读写、GPIO 和 Modem 控制功能
- 添加异常回调机制处理设备拔出等情况
- 提供 Stream 数据流支持实时串口数据监听
- 完善单元测试覆盖所有核心功能模块

example/integration_test/plugin_integration_test.dart

@@ -1,24 +1,20 @@
-// This is a basic Flutter integration test.
+// CH934X 插件的集成测试入口。
 //
-// Since integration tests run in a full Flutter application, they can interact
-// with the host side of a plugin implementation, unlike Dart unit tests.
-//
-// For more information about Flutter integration tests, please see
-// https://flutter.dev/to/integration-testing
-
-import 'package:flutter_test/flutter_test.dart';
-import 'package:integration_test/integration_test.dart';
+// 集成测试运行在完整的 Flutter 应用中,可以与原生层通信;
+// 当前插件主要覆盖 Android 平台,因此以下用例仅在连接真实
+// USB 设备时才有意义。CI 中通常会跳过该测试。
 
 import 'package:ch934x_serial/ch934x_serial.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:integration_test/integration_test.dart';
 
 void main() {
   IntegrationTestWidgetsFlutterBinding.ensureInitialized();
 
-  testWidgets('getPlatformVersion test', (WidgetTester tester) async {
+  testWidgets('plugin 暴露 deviceList API', (tester) async {
     final Ch934xSerial plugin = Ch934xSerial();
-    final String? version = await plugin.getPlatformVersion();
-    // The version string depends on the host platform running the test, so
-    // just assert that some non-empty string is returned.
-    expect(version?.isNotEmpty, true);
+    final devices = await plugin.getDeviceList();
+    // 集成测试环境下可能没有真实设备,允许为空。
+    expect(devices, isA<List<Ch934xDeviceInfo>>());
   });
 }