rust-clippy: fix remaining warnings in `hg-cpython`

rust-clippy: disable some lints crate-wide for `hg-cpython` `rust-cpython` creates some pretty funky code that also needs to be compatible with pretty old Rust. This makes clippy quite useless in `hg-cpython` unless you disable the lints that are always triggered by `py_class!` and related. Maybe `clippy` will allow one day to exclude a dependency from its linting, but this seems quite unlikely, so this is the best we've got at the moment.

rust-clippy: fix remaining warnings in `rhg` All of these are simple changes that for the most part are clear improvements and the rest are at most equivalent.

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`.

rust-nodemap: implement `PartialEq` without allocation This was caught by `clippy`. It's probable that this ends up optimized out by the compiler, but let's not rely on that.

rust-clippy: tell `clippy` we don't need to declare a default here This is a struct only useful for tests.

rust-clippy: refactor complex type This makes reading the signature a bit less tiring.

rust-clippy: simplify return type of debug function This makes the type a little bit more readable.