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.