Add proper benchmark

[Tudyx]

Right now we have benchmarks to compare with PyTorch but not really to compare ai-dataloader with itself.
It will be very useful to have some, to be able to make choices based on real data. For instance, it would help with #17, #13 and #1

There are some benchmark using the criterion library but, at least on my computer, they are too noisy to be useful. It will be useful to improve them or maybe try a different approach.

The rustls benchmarks seems very qualitative and could be a good source of inspiration.