Use `cargo-semver-checks` to validate version bumps for new releases

There are a number of changes to a Rust library that can turn out to be semver major, that may not have appeared to be at first glance.

We should use this tool as part of our release process to help avoid missed semver-major bumps:
https://github.com/obi1kenobi/cargo-semver-checks

Ideally this tool would be run as part of an automated release GitHub Action (see #595), but we could always run in manually via the releasing playbook short term:
https://github.com/heroku/libcnb.rs/blob/main/RELEASING.md

Read RELEASING.md and issue #595 first, then review how the current release process handles version bumps. Run cargo-semver-checks manually through the releasing playbook to understand the required inputs; done means semver-major changes are validated during releases, ideally by an automated GitHub Action with the manual playbook as a short-term fallback.

Written by the indexing model from the issue text.