Key-ID Serial / Recycle Scheme

[pinkforest]

It would be great to formalize a trait for a "Serial Scheme".

This is basically the key-issuing order or how the keys get generated out.

Say we could have the below traits

• Incrementing & Deterministic -> from zero to usize::MAX incrementing
• Random -> random free key
• Decreasing & Deterministic -> from usize::MAX decreasing

This is more static approach

Other could be more dynamic approach where there is introspection but I'm favoring the static one through Ext type of traits.