Actually, this is not a new requirement at all; because we do not
check the minimum version on CI, some dependencies on 1.28 have
already sneaked in. In particular, our required version of the crate
managed only works on 1.28+.

This allows us to use:
(1.28)
  - ops::RangeBounds
  - num::NonZero

Some trait bounds were added to make sure everything builds on 1.28.