rhg: upgrade `clap` dependency This one is the worst one to upgrade since v2 -> v4 broke a ton of API, which thankfully seems saner now. Contrary to what was done in the `hg-core/src/examples/nodemap` rewrite, we're not switching from the "builder" pattern to the "derive" pattern, since that would imply a much larger diff. It can be done incrementally.

hg-cpython: upgrade dependencies `hg-cpython` has no BC breaking dependencies, we can group them all in this changeset.

hg-core: upgrade all remaining dependencies Finally, these dependencies do not require any code changes, so they are all grouped in the same changeset.

hg-core: upgrade `clap` dependency Upgrading is a finally possible now that we're supporting a more recent version of Rust. This required changes in the `nodemap` example.

hg-core: upgrade `zstd` dependency Now that we support a newer version of Rust, we can update this dependency to get all the latest bugfixes and improvements. A slight API adjustment was needed.

hg-core: make use of `strip_suffix` now that we're using Rust 1.45+

rust: use `matches!` macro now that we're using Rust 1.42+

hg-core: remove unneeded util now that we support Rust 1.42+

hg-core: remove unneeded trait now that we support Rust 1.52+

rust: remove newly redundant `use` statements with the 2021 edition prelude https://doc.rust-lang.org/edition-guide/rust-2021/prelude.html