Function compare_along

pub fn compare_along(
    first: LineHit,
    second: LineHit,
) -> Result<Sign, ExactError>

Sign of t(first) - t(second): which hit comes first along their line.

Hits on different circles have different radicands; the comparison is still exact (crate::sign_two_roots). Both hits must lie on the same line, since parameters on different lines are not comparable.