impl Div<NonZeroXxx> and Rem<NonZeroXxx> for xxx

[mqudsi]

One obvious optimization that is possible with NonZeroXxx aside from simply elision of extra storage for Option<NonZeroXxx> is that it enables safe unchecked code that skips divide by zero checking.

It would be nice if, e.g., Rem<NonZeroUsize> were implemented for usize such that this would be a valid operation:

fn fast_and_safe(dividend: usize, divisor: NonZeroUsize) -> usize {
    dividend % divisor
}

This would be guaranteed panic free and there would be no need to generate the code that handles the case where divisor is zero.

[sfackler]

rust-lang/rust#79134

[mqudsi]

@sfackler thanks! I searched with a few variations of the type name and didn't find anything. (Maybe we should add a "keywords: ..." convention)