MPCNC tool mount nut trap

This is the nut trap for the MPCNC (Mostly Printed CNC by Allted) I made using the parametric design by GeoDave. I've completely rewritten the SCAD with a number of improvements, like better code re-use and clearer variable naming.

Additionally, it uses the same measurements Allted describes [in this picture](https://www.v1engineering.com/wp-content/uploads/2015/08/zrail.jpg) on [the MPCNC conduit assembly page](https://www.v1engineering.com/assembly/conduit-rails-tubes-pipes/), whereas GeoDave's design uses different ones, perhaps from an older iteration of the MPCNC.

By default, the SCAD file uses the 25mm (international "F" version) conduit with 1.5mm wall thickness, but this can easily be changed, either in the SCAD file or using the Thingiverse Customizer.

Included are STL and STEP files for the nut traps I use (1.5mm and 2.0mm wall thickness) for my own reference. The nut traps were made to fit my M4 nyloc nuts. I glued them in.

Also see the matching [drill guide](htt