Update unpretty rules to work with `rust_library_group`

[UebelAndre]

The rust_unpretty_aspect is designed to only handle targets which provide CrateInfo (and TestCrateInfo) due to the reuse of the Rustc action to pass -Zunpretty. Unfortunately, rules which provide CrateGroupInfo make it hard for rust_unpretty to spawn actions for the actual crates. It would be great if the rules could somehow handle this in a performant way.