Try another hash algorithm

[samueltardieu]

Non-user-facing data structures in pathfinding use rustc_hash as a hash function. You should investigate whether some of those usages would yield better performances if ahash was used instead. To ensure this, you should change fx* to ahash* one by one, and check with iai benchmarks (install what you need to run them) that performances improve compared to the actual baseline. Only keep improvements in your PR.