[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/examples/run_length_decoding.cu

@@ -0,0 +1,63 @@
+#include <thrust/binary_search.h>
+#include <thrust/copy.h>
+#include <thrust/device_vector.h>
+#include <thrust/gather.h>
+#include <thrust/iterator/counting_iterator.h>
+#include <thrust/scan.h>
+
+#include <iostream>
+#include <iterator>
+
+// This example decodes a run-length code [1] for an array of characters.
+//
+// [1] http://en.wikipedia.org/wiki/Run-length_encoding
+
+int main()
+{
+  // allocate storage for compressed input and run lengths
+  thrust::device_vector<char> input(6);
+  thrust::device_vector<int> lengths(6);
+
+  // clang-format off
+  input[0] = 'a';  lengths[0] = 3;
+  input[1] = 'b';  lengths[1] = 5;
+  input[2] = 'c';  lengths[2] = 1;
+  input[3] = 'd';  lengths[3] = 2;
+  input[4] = 'e';  lengths[4] = 9;
+  input[5] = 'f';  lengths[5] = 2;
+  // clang-format on
+
+  // print the initial data
+  std::cout << "run-length encoded input:" << '\n';
+  for (size_t i = 0; i < 6; i++)
+  {
+    std::cout << "(" << input[i] << "," << lengths[i] << ")";
+  }
+  std::cout << '\n' << '\n';
+
+  // scan the lengths
+  thrust::inclusive_scan(lengths.begin(), lengths.end(), lengths.begin());
+
+  // output size is sum of the run lengths
+  int N = lengths.back();
+
+  // compute input index for each output element
+  thrust::device_vector<int> indices(N);
+  thrust::lower_bound(
+    lengths.begin(),
+    lengths.end(),
+    thrust::counting_iterator<int>(1),
+    thrust::counting_iterator<int>(N + 1),
+    indices.begin());
+
+  // gather input elements
+  thrust::device_vector<char> output(N);
+  thrust::gather(indices.begin(), indices.end(), input.begin(), output.begin());
+
+  // print the initial data
+  std::cout << "decoded output:" << '\n';
+  thrust::copy(output.begin(), output.end(), std::ostream_iterator<char>(std::cout, ""));
+  std::cout << '\n';
+
+  return 0;
+}