Switch to using a watertight RMS thread cutter

The current RMS thread causes OpenSCAD to produce warnings on export. I have reimplemented an RMS thread, going back to ISO 8038-1:1997, and instead of drawing a thread directly, I model the thread cutter (i.e. something that looks like the objective thread) and subtract it from the optics module. My hope is that this should result in a watertight mesh with no joining artifacts.

I have manually checked the faces of the polyhedron all wind the right way. I believe it's about as fast as it can be, but of course there are a lot of triangles! This should be printed and tested before merging, so I'll mark as a draft until that happens.