Function orient2d_any 

pub fn orient2d_any(
    a: &ImplicitPoint,
    b: &ImplicitPoint,
    c: &ImplicitPoint,
    axis: DropAxis,
) -> Sign

orient2d over ANY mix of explicit/implicit points in ANY argument position (the predicate the re-triangulation’s point location needs). orient2d is antisymmetric, so we canonicalise the args to implicit-first (stable, to keep it a pure function), dispatch to the 0I/1I/2I/3I config, and flip the result once per transposition (the permutation parity).