Add `cargo-semver-checks`

[JonathanWoollett-Light]

Add a test using cargo-semver-checks to enforce semver.

This will require:

• [ ] Adding cargo-semver-checks to https://github.com/rust-vmm/rust-vmm-container
• [ ] Adding a test here (e.g. https://github.com/rust-vmm/rust-vmm-ci/pull/134)
• [ ] Updating https://github.com/rust-vmm/community/blob/main/docs/crate_release.md to match new workflow.

[epilys]

RFC #3516 (public/private dependencies) was merged,^1

which will help users identify when they leak their dependencies in their public API, helping prevent unintentional breaking changes. This is behind cargo-features = ["public-dependency"]. A good amount of the implementation was done as part of the superseded RFC #1977.

https://doc.rust-lang.org/cargo/reference/unstable.html#public-dependency:

public-dependency

Tracking Issue: [#44663](https://github.com/rust-lang/rust/issues/44663)

The ‘public-dependency’ feature allows marking dependencies as ‘public’ or ‘private’. When this feature is enabled, additional information is passed to rustc to allow the ‘exported_private_dependencies’ lint to function properly.

This requires the appropriate key to be set in cargo-features:

cargo-features = ["public-dependency"]

[dependencies]
my_dep = { version = "1.2.3", public = true }
private_dep = "2.0.0" # Will be 'private' by default