Explore precompiling shared `Device[Segmented][Radix]Sort` invocations serving as test-reference via extern template

The segmented top-k tests use `cub::DeviceSegmentedRadixSort` only as a verification reference. The compilation of the sort algorithm specializations is contributing a majority of the compilation time. We want to explore compiling the shared reference instantiations once and extern template-ing them in the consuming TUs. We want to explore this applicability beyond just top-k.