Diskann Benchmarking Wrapper

[tarang-jain]

Brings DiskANN into cuvs-bench

• Build and search in-memory DiskANN index
• Build and search SSD DiskANN index
• Build a cuvs Vamana index on GPU and serialize it in DiskANN format. Search on CPU using in-memory DiskANN search API.

[achirkin]

Thanks for the PR, it's nice to see the list of supported algorithms growing.

I feel unsettled though about adding new functionality to the common benchmark.hpp header just for one algorithm - this looks unsustainable. I see you probably want to avoid having the user to specify the path to the index file / dataset manually, but I think adding the new functionality in such an ad-hoc way is not a solution.
I think, the easiest solution could be just to pass both paths as algo parameters.
Maybe you can automate this in the python layer of the benchmark. Alternatively, I think it's acceptable to modify the parse_build_param api to give it access to the full json config file; that way, you could get the path to the dataset and fill-in the algo parameters inside that function.