Function chain_intersection_points 

pub fn chain_intersection_points(
    points: &[IntersectionPoint],
    threshold: f64,
) -> Vec<Vec<IntersectionPoint>>

Chain intersection points into connected components using proximity.

Points within threshold distance are considered connected. Returns ordered chains (each chain is a connected component, ordered by nearest-neighbor walk). Closed loops are detected when the last point is within threshold of the first.