Add support of build123d

[kcleung]

build123d is a python and opencascade based code-cad system that is an evolution of cadquery (which is already supported in cadhub), but has a less restrictive API:

https://build123d.readthedocs.io/en/latest/index.html

It also has several parametric parts libraries

Would be great if cadhub can extend support to build123d too.