feat: direct call download api by cgo dart

ui/flutter/lib/api/native/ffi/libgopeed_ffi.dart

@@ -0,0 +1,36 @@
+import 'dart:async';
+
+import 'package:ffi/ffi.dart';
+
+import '../libgopeed_interface.dart';
+import 'libgopeed_bind.dart';
+
+class LibgopeedFFi implements LibgopeedAbi {
+  late LibgopeedBind _libgopeed;
+
+  LibgopeedFFi(LibgopeedBind libgopeed) {
+    _libgopeed = libgopeed;
+  }
+
+  @override
+  Future<String> create(String cfg) {
+    final cfgPtr = cfg.toNativeUtf8();
+    try {
+      final result = _libgopeed.Create(cfgPtr.cast());
+      return Future.value(result.cast<Utf8>().toDartString());
+    } finally {
+      calloc.free(cfgPtr);
+    }
+  }
+
+  @override
+  Future<String> invoke(int instance, String params) {
+    final paramsPtr = params.toNativeUtf8();
+    try {
+      final result = _libgopeed.Invoke(instance, paramsPtr.cast());
+      return Future.value(result.cast<Utf8>().toDartString());
+    } finally {
+      calloc.free(paramsPtr);
+    }
+  }
+}