`zvariant` is unmaintained

The `zvariant` crate is no longer maintained as a standalone crate.

It has been merged into [`zbus`](https://crates.io/crates/zbus) starting with version `6.0.0`, as its `wire` module.

Users should migrate to [`zbus`](https://crates.io/crates/zbus), with its default features disabled if they only need the D-Bus wire format. Users of the GVariant format should migrate to [`zgvariant`](https://crates.io/crates/zgvariant).