completed velocity integration

lib/models/api_response.dart

@@ -0,0 +1,21 @@
+class ApiResponse<T> {
+  final T? data;
+  final String? error;
+  final int? statusCode;
+
+  const ApiResponse({
+    this.data,
+    this.error,
+    this.statusCode,
+  });
+
+  bool get isSuccess => error == null && data != null;
+
+  factory ApiResponse.success(T data, {int? statusCode}) {
+    return ApiResponse(data: data, statusCode: statusCode);
+  }
+
+  factory ApiResponse.failure(String error, {int? statusCode}) {
+    return ApiResponse(error: error, statusCode: statusCode);
+  }
+}