Type Alias AutoSpaceVec2

Detect enclosed regions from a set of 2D wall axis segments.

Pipeline:

1. Snap close vertices within snapTolerance (collapses tiny gaps between wall ends that should meet at a corner).
2. Resolve pairwise segment intersections — each crossing splits both segments into shorter pieces meeting at the new vertex.
3. Build a half-edge graph (DCEL): every undirected segment becomes two opposing directed half-edges; per vertex, the half-edges leaving it are ordered by polar angle so we can find the next CCW-around-a-face neighbour in O(1).
4. Walk minimum cycles by always taking the leftmost turn. Each half-edge belongs to exactly one face cycle.
5. Drop the outer (unbounded) face — the one with the most- negative signed area.
6. Filter the remaining faces by minArea.

Pure: no IFC dependencies. Output is a list of CCW polygons (outline) plus the signed area of each. Callers feed these into the per-storey IfcSpace builder.