[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/libcudacxx/include/cuda/std/climits

@@ -0,0 +1,61 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of libcu++, the C++ Standard Library for your entire system,
+// under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2023 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _CUDA_STD_CLIMITS
+#define _CUDA_STD_CLIMITS
+
+#include <cuda/std/detail/__config>
+
+#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
+
+#if _CCCL_HOSTED()
+#  include <climits>
+#else // ^^^ _CCCL_HOSTED() ^^^ / vvv _CCCL_FREESTANDING() vvv
+#  define _CCCL_CHAR_IS_UNSIGNED() ('\xff' > 0) // CURSED
+
+#  define CHAR_BIT 8
+
+#  define SCHAR_MIN (-128)
+#  define SCHAR_MAX 127
+#  define UCHAR_MAX 255
+
+#  if _CCCL_CHAR_IS_UNSIGNED()
+#    define CHAR_MIN 0
+#    define CHAR_MAX UCHAR_MAX
+#  else
+#    define CHAR_MIN SCHAR_MIN
+#    define CHAR_MAX SCHAR_MAX
+#  endif
+#  define SHRT_MIN  (-SHRT_MAX - 1)
+#  define SHRT_MAX  0x7fff
+#  define USHRT_MAX 0xffff
+#  define INT_MIN   (-INT_MAX - 1)
+#  define INT_MAX   0x7fffffff
+#  define UINT_MAX  0xffffffff
+#  define LONG_MIN  (-LONG_MAX - 1)
+#  ifdef __LP64__
+#    define LONG_MAX  LLONG_MAX
+#    define ULONG_MAX ULLONG_MAX
+#  else
+#    define LONG_MAX  INT_MAX
+#    define ULONG_MAX UINT_MAX
+#  endif
+#  define LLONG_MIN  (-LLONG_MAX - 1)
+#  define LLONG_MAX  0x7fffffffffffffffLL
+#  define ULLONG_MAX 0xffffffffffffffffUL
+#endif // _CCCL_FREESTANDING()
+
+#endif // _CUDA_STD_CLIMITS