Add unconditionally implemented (potentially) open-ended bounds

[tyilo]

I have a use-case for a function supporting both big integers and primitive integers. It would be useful to be able to get the minimum and maximum value as an Option<T> at runtime, without having to use a generic info.

Type	Bounds
BigInt	..
BigUInt	0..
T: Bounded	T::min_value()..=T::max_value()

This could be implemented as:

trait FiniteRange {
    fn min_value() -> Option<Self>;
    fn max_value() -> Option<Self>;
}