[INFRA] Import NVIDIA/CCCL upstream as optimization reference library

CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0

cccl_upstream/cub/cub/cub.cuh

@@ -0,0 +1,98 @@
+// SPDX-FileCopyrightText: Copyright (c) 2011, Duane Merrill. All rights reserved.
+// SPDX-FileCopyrightText: Copyright (c) 2011-2018, NVIDIA CORPORATION. All rights reserved.
+// SPDX-License-Identifier: BSD-3
+
+/**
+ * \file
+ * CUB umbrella include file
+ */
+
+#pragma once
+
+// Static configuration
+#include <cub/config.cuh>
+
+#ifndef CCCL_DISABLE_NVRTC_COMPATIBILITY_CHECK
+#  if _CCCL_COMPILER(NVRTC)
+#    error \
+      "Including <cub/cub.cuh> is not supported when compiling with NVRTC. Include the specific device header instead (e.g. <cub/block/block_reduce.cuh>). You can define CCCL_DISABLE_NVRTC_COMPATIBILITY_CHECK to disable this warning."
+#  endif // _CCCL_COMPILER(NVRTC)
+#endif // CCCL_DISABLE_NVRTC_COMPATIBILITY_CHECK
+
+#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
+#  pragma GCC system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
+#  pragma clang system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
+#  pragma system_header
+#endif // no system header
+
+// Block
+#include <cub/block/block_adjacent_difference.cuh>
+#include <cub/block/block_discontinuity.cuh>
+#include <cub/block/block_exchange.cuh>
+#include <cub/block/block_histogram.cuh>
+#include <cub/block/block_load.cuh>
+#include <cub/block/block_merge_sort.cuh>
+#include <cub/block/block_radix_rank.cuh>
+#include <cub/block/block_radix_sort.cuh>
+#include <cub/block/block_reduce.cuh>
+#include <cub/block/block_scan.cuh>
+#include <cub/block/block_store.cuh>
+// #include <cub/block/block_shift.cuh>
+
+// Device
+#include <cub/device/device_adjacent_difference.cuh>
+#include <cub/device/device_batched_topk.cuh>
+#include <cub/device/device_copy.cuh>
+#include <cub/device/device_find.cuh>
+#include <cub/device/device_for.cuh>
+#include <cub/device/device_histogram.cuh>
+#include <cub/device/device_memcpy.cuh>
+#include <cub/device/device_merge.cuh>
+#include <cub/device/device_merge_sort.cuh>
+#include <cub/device/device_partition.cuh>
+#include <cub/device/device_radix_sort.cuh>
+#include <cub/device/device_reduce.cuh>
+#include <cub/device/device_run_length_encode.cuh>
+#include <cub/device/device_scan.cuh>
+#include <cub/device/device_segmented_radix_sort.cuh>
+#include <cub/device/device_segmented_reduce.cuh>
+#include <cub/device/device_segmented_sort.cuh>
+#include <cub/device/device_select.cuh>
+#include <cub/device/device_topk.cuh>
+#include <cub/device/device_transform.cuh>
+
+// Grid
+#include <cub/grid/grid_even_share.cuh>
+#include <cub/grid/grid_mapping.cuh>
+#include <cub/grid/grid_queue.cuh>
+
+// Thread
+#include <cub/thread/thread_load.cuh>
+#include <cub/thread/thread_operators.cuh>
+#include <cub/thread/thread_reduce.cuh>
+#include <cub/thread/thread_scan.cuh>
+#include <cub/thread/thread_store.cuh>
+
+// Warp
+#include <cub/warp/warp_exchange.cuh>
+#include <cub/warp/warp_load.cuh>
+#include <cub/warp/warp_merge_sort.cuh>
+#include <cub/warp/warp_reduce.cuh>
+#include <cub/warp/warp_scan.cuh>
+#include <cub/warp/warp_store.cuh>
+
+// Iterator
+#include <cub/iterator/arg_index_input_iterator.cuh>
+#include <cub/iterator/cache_modified_input_iterator.cuh>
+#include <cub/iterator/cache_modified_output_iterator.cuh>
+#include <cub/iterator/tex_obj_input_iterator.cuh>
+
+// Util
+#include <cub/util_allocator.cuh>
+#include <cub/util_debug.cuh>
+#include <cub/util_device.cuh>
+#include <cub/util_ptx.cuh>
+#include <cub/util_temporary_storage.cuh>
+#include <cub/util_type.cuh>