Constructive solid geometry - union, intersection, difference

It would be good to be able to set each shape as union, intersection or difference, for modelling complex shapes. Here is a more in depth explanation - https://en.wikipedia.org/wiki/Constructive_solid_geometry

Also handy are extrusions - https://www.sciencedirect.com/topics/engineering/path-extrusion

Start by reviewing the issue's Constructive Solid Geometry and path-extrusion references, then inspect the repository's existing shape and modeling entry points. Done would require a defined, tested approach for union, intersection, difference, and extrusion support, but the issue names no files or tests.

Written by the indexing model from the issue text.