Introduce Swiss Cheese benchmark

[matthieu-m]

• Changes:

• Introduce new swiss_cheese.rs benchmark.

• Motivation:

The current design of RawTable leaves tombstones behind to indicate deleted elements, going from tightly packed elements to a much more sparse design as more and more elements are deleted -- until more elements are inserted again, at least.

This creates a "swiss cheese" situation, with a decreasing elements density over time. This situation is expected to lead to a higher number of cache misses as this density decreases.

The swiss_cheese.rs benchmark suite aims at measuring the impact of this effect on performance.

[Amanieu]

CI should be fixed now, can you rebase? I am curious to see what kind of results you are getting with this benchmark.

[Amanieu]

With that said, I don't think it makes sense to merge this benchmark. It is useful as an experiment, but it's less useful for measuring the actual performance of the table.

[matthieu-m]

I don't think it makes much sense either.

Making a PR was the easiest to share both code and result, but it may be a bit too specific.