pub fn subtract_ristretto(
left_point: &PodRistrettoPoint,
right_point: &PodRistrettoPoint,
) -> Option<PodRistrettoPoint>
pub fn subtract_ristretto(
left_point: &PodRistrettoPoint,
right_point: &PodRistrettoPoint,
) -> Option<PodRistrettoPoint>