fix: `rust-toolchain` and `crane` use in flake

[eureka-cpu]

The flake doesn't seem to take advantage of some of the core features of crane, one of them being how you can inherit a cargo toolchain from checks. It could look more like https://github.com/Cloud-Scythe-Labs/cargo-reaper/blob/281a9de1b41941aea18e7838706660b21e649fd9/flake.nix#L396 where each check is its own derivation built with its corresponding cargo tool, and they become part of the developer environment. The rust -toolchain doesn't contain anything other than the rust version, but it could be a rust-toolchain.toml where we declare the toolchain components we want as part of the devShell: https://github.com/Cloud-Scythe-Labs/cargo-reaper/blob/281a9de1b41941aea18e7838706660b21e649fd9/flake.nix#L48

[eureka-cpu]

Also recommend replacing oxalica with fenix

[eureka-cpu]

if openssl isn't a hard dependency, maybe consider using rustls features in the cargo dependencies if they are available, then checking if they can't be satisfied using autoPatchelfHook in the nativeBuildInputs for linux systems.

[eureka-cpu]

The pre-commit can also be removed once the crane checks are added, since they run the same checks as derivations using the provided toolchain.