Add build123d v0.7.0

[erooke]

Adds an expression for build123d. To do this expressions had to be added for svgpathtools, ocpsvg, py-lib3mf, and trianglesolver.

At the moment nixpkgs has lib3mf 2.2.0 packaged. For ease of making it work asap I followed suit. This meant building py-lib3mf version 2.2.0 and only building version 0.4.0 of build123d (current is 0.5.0).

Would close #41.