[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/cmake/CubCudaConfig.cmake

@@ -0,0 +1,62 @@
+#
+# Architecture options:
+#
+
+option(
+  CUB_ENABLE_RDC_TESTS
+  "Enable tests that require separable compilation."
+  ON
+)
+option(
+  CUB_FORCE_RDC
+  "Enable separable compilation on all targets that support it."
+  OFF
+)
+
+option(
+  CUB_ENABLE_LAUNCH_NO_LAUNCHER
+  "Enable tests/examples without explicit launch variants."
+  ON
+)
+option(
+  CUB_ENABLE_LAUNCH_HOST_LAUNCHER
+  "Enable host launch variants (lid_0)."
+  ON
+)
+option(
+  CUB_ENABLE_LAUNCH_DEVICE_LAUNCHER
+  "Enable device launch variants (lid_1)."
+  ON
+)
+option(
+  CUB_ENABLE_LAUNCH_GRAPH_LAUNCHER
+  "Enable graph launch variants (lid_2)."
+  ON
+)
+
+option(
+  CUB_ENABLE_LAUNCH_VARIANTS
+  "Deprecated: use CUB_ENABLE_LAUNCH_DEVICE_LAUNCHER/GRAPH_LAUNCHER to control lid_1/lid_2."
+  ON
+)
+
+if (NOT CUB_ENABLE_LAUNCH_VARIANTS)
+  message(
+    WARNING
+    "CUB_ENABLE_LAUNCH_VARIANTS is deprecated; disabling lid_1/lid_2 launch variants."
+  )
+  set(
+    CUB_ENABLE_LAUNCH_DEVICE_LAUNCHER
+    OFF
+    CACHE BOOL
+    "Enable device launch variants (lid_1)."
+    FORCE
+  )
+  set(
+    CUB_ENABLE_LAUNCH_GRAPH_LAUNCHER
+    OFF
+    CACHE BOOL
+    "Enable graph launch variants (lid_2)."
+    FORCE
+  )
+endif()