[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/c/experimental/stf/test/test_token.cpp

@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of CUDA Experimental in CUDA C++ Core Libraries,
+// 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) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cuda_runtime.h>
+
+#include <c2h/catch2_test_helper.h>
+#include <cccl/c/experimental/stf/stf.h>
+
+C2H_TEST("stf token", "[token]")
+{
+  stf_ctx_handle ctx = stf_ctx_create();
+  REQUIRE(ctx != nullptr);
+
+  stf_logical_data_handle lX = stf_token(ctx);
+  stf_logical_data_handle lY = stf_token(ctx);
+  stf_logical_data_handle lZ = stf_token(ctx);
+  REQUIRE(lX != nullptr);
+  REQUIRE(lY != nullptr);
+  REQUIRE(lZ != nullptr);
+
+  stf_logical_data_set_symbol(lX, "X");
+  stf_logical_data_set_symbol(lY, "Y");
+  stf_logical_data_set_symbol(lZ, "Z");
+
+  stf_task_handle t1 = stf_task_create(ctx);
+  REQUIRE(t1 != nullptr);
+  stf_task_set_symbol(t1, "T1");
+  stf_task_add_dep(t1, lX, STF_RW);
+  stf_task_start(t1);
+  stf_task_end(t1);
+  stf_task_destroy(t1);
+
+  stf_task_handle t2 = stf_task_create(ctx);
+  REQUIRE(t2 != nullptr);
+  stf_task_set_symbol(t2, "T2");
+  stf_task_add_dep(t2, lX, STF_READ);
+  stf_task_add_dep(t2, lY, STF_RW);
+  stf_task_start(t2);
+  stf_task_end(t2);
+  stf_task_destroy(t2);
+
+  stf_task_handle t3 = stf_task_create(ctx);
+  REQUIRE(t3 != nullptr);
+  stf_task_set_symbol(t3, "T3");
+  stf_task_add_dep(t3, lX, STF_READ);
+  stf_task_add_dep(t3, lZ, STF_RW);
+  stf_task_start(t3);
+  stf_task_end(t3);
+  stf_task_destroy(t3);
+
+  stf_task_handle t4 = stf_task_create(ctx);
+  REQUIRE(t4 != nullptr);
+  stf_task_set_symbol(t4, "T4");
+  stf_task_add_dep(t4, lY, STF_READ);
+  stf_task_add_dep(t4, lZ, STF_RW);
+  stf_task_start(t4);
+  stf_task_end(t4);
+  stf_task_destroy(t4);
+
+  stf_logical_data_destroy(lX);
+  stf_logical_data_destroy(lY);
+  stf_logical_data_destroy(lZ);
+
+  stf_ctx_finalize(ctx);
+}