Allow running as cargo-mutest & cargo mutest

[seam345]

Taking inspiration from cargo insta
https://github.com/mitsuhiko/insta/blob/7f23d2e4684a789a85c50503004fb38a23c9ea58/cargo-insta/src/cli.rs#L1656

[zalanlevai]

Thank you for this! I have been meaning to make this change for a while and had done it not long ago in #7 (specifically commit 9194559 for the standalone invocation of cargo-mutest). Could you please take a look at this and see if it serves the same purpose as this PR? #7 also made changes that make standalone invocations of mutest-driver much easier, although the right toolchain version still needs to be set up (i.e., rustup run nightly-2025-11-26 mutest-driver --help), otherwise mutest-driver fails to load with dynamic linker errors on rustc-driver.

Are there any remaining outstanding changes that would make Nix compatibility easier?

[zalanlevai]

RE #7: Do note that it makes some relatively significant changes to the user-facing CLI, but not in a way that should make a big difference to Nix compatibility.

[seam345]

Oh I was wondering if you was going to make the change in #7 but didn't see it in the write-up, was originally just going to make an issue but when I saw how cargo insta did it i thought it was better to just whip up a PR :)

Anyway yep updated hash and it works in my nix build \o/ tbh I think it's more a thing I wanted than nix wants