[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/thrust/cmake/ThrustFindThrust.cmake

@@ -0,0 +1,42 @@
+function(_thrust_find_thrust_multiconfig)
+  # Check which systems are enabled by multiconfig:
+  set(req_systems)
+  if (THRUST_MULTICONFIG_ENABLE_SYSTEM_CUDA)
+    list(APPEND req_systems CUDA)
+  endif()
+  if (THRUST_MULTICONFIG_ENABLE_SYSTEM_CPP)
+    list(APPEND req_systems CPP)
+  endif()
+  if (THRUST_MULTICONFIG_ENABLE_SYSTEM_TBB)
+    list(APPEND req_systems TBB)
+  endif()
+  if (THRUST_MULTICONFIG_ENABLE_SYSTEM_OMP)
+    list(APPEND req_systems OMP)
+  endif()
+
+  find_package(
+    Thrust
+    REQUIRED
+    CONFIG
+    NO_DEFAULT_PATH # Only check the explicit path in HINTS:
+    HINTS "${CCCL_SOURCE_DIR}/lib/cmake/thrust/"
+    COMPONENTS ${req_systems}
+  )
+endfunction()
+
+function(_thrust_find_thrust_singleconfig)
+  cccl_get_thrust()
+
+  # Create target now to prepare system found flags:
+  thrust_create_target(thrust.config FROM_OPTIONS ${THRUST_TARGET_FLAGS})
+  thrust_debug_target(thrust.config "${THRUST_VERSION}")
+endfunction()
+
+# Find thrust along with all requested backends.
+function(thrust_find_thrust)
+  if (THRUST_ENABLE_MULTICONFIG)
+    _thrust_find_thrust_multiconfig()
+  else()
+    _thrust_find_thrust_singleconfig()
+  endif()
+endfunction()