rdev: add option to turn off stubgen

[TheTripleV]

No description provided.

[virtuald]

There is already an environment variable in robotpy-build to suppress stubgen building.

[TheTripleV]

Right, but since there's actual tooling now, all the options should be configurable through the tooling. So I don't have to manually set environment variables every time I open a new terminal (and no, I don't want to globally set robotpy build options only to forget about em in the future)