[BUG] cuvs-bench recipe doesn't have a dependency on cuvs Python, but create_groundtruth requires it.

[cjnolet]

I think we could get around 2 issues here:

1. The cuvs-bench-cpu cannot use the gpu to generate ground truth
2. The cuvs-bench doesn't have a hard dependnecy on cuvs python, even though it assumes it's installed to create_groundtruth.

We should test if cuvs is installed in the python environment, and if not, issue a warning that the ground truth could be much faster if cuvs were installed. Then we should fall back to numpy.