rust-clippy: fix most warnings in `hg-core` All of these are simple changes that for the most part are clear improvements and the rest are at most equivalent. The remaining warnings have to be fixed either with a bigger refactor like for the nested "revlog" module, or in the dependency `bytes-cast`, which we own. This will be done sometime in the future.

rust-utils: strip redundant prefix from enum This was highlighted by `clippy`, I think this makes the code cleaner.

rust-filepatterns: don't `Box` subincludes unnecessarily This was caught by `clippy`.