Add badges for unmaintained and UB containing crates

[fereidani]

I think there should be clear, visible guidance to help users understand the quality of the crates they import.

I see many widely used crates that are unmaintained, or there are crates whose maintainers are aware of undefined behavior existence but refuse/reject to fix it.

I suggest adding two colored badges "unmaintained" and "undefined-behavior", so users are clearly warned before using such crates. If the situation changes, the maintainer should be able to request that the badges be removed.

I'm not sure how report/assign process should be, But I believe implementing this would benefit Rust community and forces the maintainers to hold to rust safety standard.

It could be a semi-automated system with human review that if a user/researcher submits a safe API test that wouldn't pass miri, after a grace period that badge would be placed on that crate if issue is not resolved by the maintainer.