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

rust: move all crates in the main workspace to edition 2021 We've changed our minimum Rust version to 1.61.0 in the previous patch, and edition 2021 predates that version.

rust: upgrade supported Rust toolchain version A few months ago¹, a decision was made to move the Rust toolchain target to whatever Debian Testing was tracking. I didn't have the bandwidth to act on it until now. This is starting to be even more problematic than before, now that edition 2021 is out. The CI has been updated to track the current Debian testing version, 1.61.0. [1] https://lists.mercurial-scm.org/pipermail/mercurial-packaging/2022-April/000338.html

branching: merge stable into default