chore: import upstream snapshot with attribution

paddle/phi/api/include/compat/c10/util/complex.h

@@ -0,0 +1,29 @@
+// Copyright (c) 2025 PaddlePaddle Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include "paddle/phi/common/complex.h"
+
+namespace c10 {
+template <typename T>
+using complex = ::phi::dtype::complex<T>;
+}  // namespace c10
+
+namespace at {
+using c10::complex;
+}  // namespace at
+namespace torch {
+using c10::complex;
+}  // namespace torch