Composite
Marker for a shape built from blades by composition — not itself a CGA element.
Implemented by Segment, Polyline, and Polygon. A composite holds its Primitives — a wrapped blade whose accessors it forwards (Segment) or a vertex list with derived edges (Polyline, Polygon) — converting explicitly where a single algebra counterpart exists (Segment.toDipole). Sealed, so a when over a Composite is exhaustive without an else — a new composite is a compile error at every dispatch site.