Uses FXHash, rather than Rust's default hasher

[sts10]

Uses FxHash rather than Rust's default hasher, in an attempt to improve performance.

My tests have been a bit inconclusive, so would appreciate it if others compared these changes to the main branch in whatever way they think best. FxHash might even be a touch slower in some cases? I'm not sure.

There are definitely other hashers that may be worth exploring, like ahash. Maybe alternatives to try can be discussed in the comments here.

[sirwart]

Hey Sam, I would be very surprised if the choice of hash map had an effect on overall performance. Most of the time should be spent looking for regex matches in files, since you're looking for a small number of needles in a very large haystack. If the code for determining whether a needle is actually a secret or not is running slow then I would guess that it's caused by the algorithm being slow (i.e something being accidentally exponential instead of linear). If that's the case, I think the algorithm would need to be fixed rather than the hash map implementation.

Given the built-in hash map has reasonably fast performance, I would prefer to stick with the built-in hash map and not add an additional dependency.

While benchmarks are useful for seeing whether an optimization worked or not, I think profiling is a good way to highlight which parts of the system are worth optimizing. However before even doing that, I would wait until there's a case where ripsecrets runs unreasonably slowly for some input (which I'm sure there are edge cases where it does) since that will likely be a case where optimization is helpful.

[sts10]

Ah, thanks for the explanation! Think I was a bit overeager to make more contributions.

[sirwart]

No problem, your contributions have been greatly appreciated! I'm mostly waiting for more feedback for folks in terms of what improvements are needed, but there are still a few small improvements that I'm aware of. I filed them all in the issue tracker https://github.com/sirwart/ripsecrets/issues in case any of them peaked your interest.