fix: 修复特征提取失败(错误码81929)

问题: extractFaceFeature 返回错误码 81929 (MERR_FSDK_FACEFEATURE_FACEDATA)

根本原因: detectFaces 返回的人脸信息缺少 faceData 字段，
而虹软 SDK 的 extractFaceFeature 必须要有这个字段才能提取特征

修复:
- FaceEngineManager.convertFaceInfoToList: 添加返回 faceData
- ArcPlugin.handleExtractFaceFeature: 接收并传递 faceData 参数
- Dart API: extractFaceFeature 添加 faceData 参数
- example: 传递 faceData 到特征提取调用

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/arc_test.dart

@@ -0,0 +1,89 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:arc/arc.dart';
+import 'package:arc/arc_platform_interface.dart';
+import 'package:arc/arc_method_channel.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+import 'dart:typed_data';
+
+class MockArcPlatform
+    with MockPlatformInterfaceMixin
+    implements ArcPlatform {
+
+  @override
+  Future<String?> getPlatformVersion() => Future.value('42');
+
+  @override
+  Future<Map<String, dynamic>?> activeOnline({
+    required String appId,
+    required String sdkKey,
+    required String activeKey,
+  }) => Future.value({'success': true, 'errorCode': 0, 'message': 'success'});
+
+  @override
+  Future<Map<String, dynamic>?> init({
+    int? detectMode,
+    int? orient,
+    int? maxFaceNum,
+    int? combinedMask,
+  }) => Future.value({'success': true, 'errorCode': 0, 'message': 'success'});
+
+  @override
+  Future<Map<String, dynamic>?> detectFaces({
+    required Uint8List data,
+    required int width,
+    required int height,
+    int format = 2050,
+  }) => Future.value({'success': true, 'errorCode': 0, 'faceList': [], 'rgbLiveness': 1, 'isRgbAlive': true});
+
+  @override
+  Future<Map<String, dynamic>?> extractFaceFeature({
+    required Uint8List data,
+    required int width,
+    required int height,
+    required int rectLeft,
+    required int rectTop,
+    required int rectRight,
+    required int rectBottom,
+    int format = 2050,
+    int faceOrientation = 0,
+    int faceId = -1,
+    Uint8List? faceData,
+    int extractType = 1,
+    int mask = 0,
+  }) => Future.value({'success': true, 'errorCode': 0, 'featureData': Uint8List(512)});
+
+  @override
+  Future<Map<String, dynamic>?> compareFaceFeature({
+    required Uint8List featureData1,
+    required Uint8List featureData2,
+    int compareModel = 0,
+  }) => Future.value({'success': true, 'errorCode': 0, 'similarity': 0.95});
+
+  @override
+  Future<Map<String, dynamic>?> registerFaceFeature({
+    required int searchId,
+    required Uint8List featureData,
+    String? faceTag,
+  }) => Future.value({'success': true, 'errorCode': 0, 'message': 'success'});
+
+  @override
+  Future<Map<String, dynamic>?> registerFaceFeatureBatch({
+    required List<Map<String, dynamic>> faceList,
+  }) => Future.value({'success': true, 'errorCode': 0, 'message': 'success'});
+}
+
+void main() {
+  final ArcPlatform initialPlatform = ArcPlatform.instance;
+
+  test('$MethodChannelArc is the default instance', () {
+    expect(initialPlatform, isInstanceOf<MethodChannelArc>());
+  });
+
+  test('getPlatformVersion', () async {
+    Arc arcPlugin = Arc();
+    MockArcPlatform fakePlatform = MockArcPlatform();
+    ArcPlatform.instance = fakePlatform;
+
+    expect(await arcPlugin.getPlatformVersion(), '42');
+  });
+}