Dividing a span by a span

[SpookyYomo]

use jiff::{Span, SpanRound, ToSpan, Unit};

fn main() {
    let dt1: Span = 5.nanoseconds();
    let dt2: Span = 5.microseconds()
    let y = 40_000 * dt1;
    // let n = y / dt2; // error!
    
    let squeeze_to_ns = SpanRound::new()
        .smallest(Unit::Nanosecond)
        .largest(Unit::Nanosecond);
    // would be great to programatically determine the smaller of units between dt2 and y
    let n = y.round(squeeze_to_ns).unwrap().get_nanoseconds()
        / x.round(squeeze_to_ns).unwrap().get_nanoseconds();
}

Is this the best way so far?
The long and short of it is to say, let's say I have a time series of data and suppose I have some dt between each sample; as an example.

[BurntSushi]

That probably seems right, although it might be a little simpler with Span::total.

This might also be a good use case for SignedDuration, which is being added in #86.