refactor(android): 重构Android端实现使用官方SDK替代反射调用

- 移除反射机制，直接集成CH934XLib.jar官方SDK
- 添加CH934XManager初始化逻辑并处理Application上下文兼容性
- 实现设备枚举、串口打开关闭等核心功能的直接调用
- 集成IDataCallback和IModemStatus回调处理
- 更新异常回调机制，支持原生层主动推送异常事件
- 优化设备连接状态管理和USB权限处理
- 为Dart模型类添加相等性比较和哈希码实现
- 更新示例应用UI以适配新的串口索引选择逻辑

lib/ch934x_serial_method_channel.dart

@@ -21,6 +21,22 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
   final StreamController<Ch934xException> _exceptionController =
       StreamController<Ch934xException>.broadcast();
 
+  /// 接收来自原生层主动调用的 `onException` 消息。
+  Future<void> _onNativeMethodCall(MethodCall call) async {
+    if (call.method == 'onException') {
+      final args = call.arguments;
+      if (args is Map) {
+        _exceptionController.add(
+          Ch934xException(
+            type: (args['type'] as int?) ?? Ch934xExceptionType.unknown,
+            message: args['message'] as String?,
+            cause: args['cause'] as String?,
+          ),
+        );
+      }
+    }
+  }
+
   @override
   Future<List<Ch934xDeviceInfo>> getDeviceList() async {
     final raw = await methodChannel.invokeMethod<List<dynamic>>('getDeviceList');
@@ -86,6 +102,18 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
     return result ?? false;
   }
 
+  @override
+  Future<bool> setActivePort(int serialPortIndex) async {
+    if (serialPortIndex < 0) {
+      return false;
+    }
+    final result = await methodChannel.invokeMethod<bool>(
+      'setActivePort',
+      <String, Object>{'serialPortIndex': serialPortIndex},
+    );
+    return result ?? false;
+  }
+
   @override
   Future<Uint8List> read(int length) async {
     if (length <= 0) {
@@ -156,6 +184,8 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
   Future<void> setExceptionCallback(
     void Function(Ch934xException exception) onException,
   ) async {
+    // 注册接收原生层主动推送的 `onException` 事件。
+    methodChannel.setMethodCallHandler(_onNativeMethodCall);
     _exceptionController.stream.listen(onException);
     await methodChannel.invokeMethod<void>('setExceptionCallback');
   }