Consider porting over to bounded-integer crate

[chrysn]

Features similar to uX are being provided by the bounded-integer crate; in particular, AIU they solved the niche topic that @Kijewski proposed in #49 and that got stuck in review.

I have not tried out that crate, so the outcome of whether this is even practical is very open, but if nothing else, we're short-staffed here, and any way of reducing the number of places where new features (eg. stdlib methods on numbers) are added would be good.