Initial snapshot: hand motion pipeline (Dyn-HaMR + dex-retargeting + SPIDER)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

third_party/vipe/csrc/utils_ext/platform.h

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+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * 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
+
+#if defined(__CUDACC__) && defined(__CUDA_ARCH__)
+#define _CPU_AND_GPU_CODE_ __host__ __device__  // for CUDA device code
+#else
+#define _CPU_AND_GPU_CODE_
+#endif
+
+#if defined(__CUDACC__)
+#define _CPU_AND_GPU_CODE_TEMPLATE_ __host__ __device__  // for CUDA device code
+#else
+#define _CPU_AND_GPU_CODE_TEMPLATE_
+#endif
+
+#if defined(__CUDACC__) && defined(__CUDA_ARCH__)
+#define _CPU_AND_GPU_CONSTANT_ __constant__  // for CUDA device code
+#else
+#define _CPU_AND_GPU_CONSTANT_ const
+#endif
+
+#if defined(__CUDACC__) && defined(__CUDA_ARCH__)
+#include <THC/THCAtomics.cuh>
+
+template <typename ScalarT>
+static inline __device__ void atomicAdd(ScalarT* addr, ScalarT value) {
+    gpuAtomicAddNoReturn(addr, value);
+}
+#else
+template <typename ScalarT>
+static inline void atomicAdd(ScalarT* addr, ScalarT value) {
+    *addr += value;
+}
+#endif