[WIP][Test, Please ignore] Investigate performance impact of using multiprocessing only
`multiprocess` uses `dill` instead of `pickle` for pickling shared objects and, as such, can pickle more types than `multiprocessing`. And I don't think this is something we want to change :). That makes sense to me, and I don't think you should merge this change. I was only curious about the performance impact. I saw the benchmarks that was produced in other PRs, and wanted to get a better understanding of it. I created this PR to see if it got automatically added here.

Is there a way I can generate those benchmarks myself? You can find some speed comparisons between dill and pickle on SO if you google "dill vs pickle speed".

And for the benchmarks, you can generate them locally with DVC running this code from the repo root: https://github.com/huggingface/datasets/blob/0803a006db1c395ac715662cc6079651f77c11ea/.github/workflows/benchmarks.yaml#L23-L47. Thanks for the help @mariosasko!