feat: direct call download api by cgo dart

ui/flutter/lib/api/native/channel/libgopeed_channel.dart

@@ -0,0 +1,24 @@
+import 'package:flutter/services.dart';
+
+import '../libgopeed_interface.dart';
+
+class LibgopeedChannel implements LibgopeedAbi {
+  static const _channel = MethodChannel('gopeed.com/libgopeed');
+
+  @override
+  Future<String> create(String cfg) async {
+    final result = await _channel.invokeMethod<String>('create', {
+      'cfg': cfg,
+    });
+    return result!;
+  }
+
+  @override
+  Future<String> invoke(int instance, String params) async {
+    final result = await _channel.invokeMethod<String>('invoke', {
+      'instance': instance,
+      'params': params,
+    });
+    return result!;
+  }
+}