Use `rustc-hash` instead of `fxhash`

[0xbe7a]

Some data types in Rattler, like rattler_conda_types::RepoData, use FxHashMap instead of HashMap for better performance. This implementation utilizes fxhash, which employs a simpler hash function compared to the default one from std. fxhash was originally extracted from rustc, and since then, rustc-hash has been created and is maintained by rust-lang.

fxhash has not seen a release in seven years, and the last commit was five years ago. In contrast, rustc-hash is under active maintenance.

The author himself recommends using rustc-hash instead, as stated in https://github.com/cbreeden/fxhash/issues/10. As downstream users of this library have to interact with FxHashMaps, I think it would make sense to switch over to rustc-hash to avoid forcing people to depend on outdated crates and use the more popular crate instead.