Add test for explicit user-side NVTX API use

cub/test/test_nvtx_in_usercode_explicit.cu

@@ -0,0 +1,17 @@
+#define NVTX3_CPP_REQUIRE_EXPLICIT_VERSION
+#include <cub/device/device_for.cuh> // internal include of NVTX
+
+#include <thrust/iterator/counting_iterator.h>
+
+#include <cuda/std/functional>
+
+#include <nvtx3/nvtx3.hpp> // user-side include of NVTX, retrieved elsewhere
+
+int main()
+{
+  nvtx3::v1::scoped_range range("user-range"); // user-side use of explicit NVTX API
+
+  thrust::counting_iterator<int> it{0};
+  cub::DeviceFor::ForEach(it, it + 16, ::cuda::std::negate<int>{}); // internal use of NVTX
+  cudaDeviceSynchronize();
+}