Make rustfmt optional

[Jannik2099]

It would be much appreciated if SkeletonBuilder could be configured with .rustfmt(None)

Rustup offers various profiles (minimal, default, complete), and rustfmt is not part of the minimal profile. However, there's really no need for it in CI builds and such (and ideally, you don't vendor generated code anyways).

[d-e-s-o]

It shouldn't be required as per 4c2e9bb, though I can imagine rustup messing around saying the component is not installed or so.

That being said, I agree that providing an explicit opt-out would be cleaner. Are you interested in contributing a fix?

[Jannik2099]

Oh darn, rustup install a rustfmt stub that tells you to install it if needed.
Whoever thought this was a good idea? sigh

As for the opt-out, do you think modifying SkeletonBuilder::rustfmt to take an Option<...> is suitable, or do you prefer an explicit SkeletonBuilder::run_rustfmt(bool) ?

[d-e-s-o]

Adjusting SkeletonBuilder::rustfmt to take an Option seems most straight forward (from a user point of view) to me.