Add dart infrastructure to CI
c.f. https://github.com/adsharma/py2many/issues/44 , the print.dart depends on sprintf being pre-installed, and dart needs to be added to GitHub actions, which then also acts as a reference for people wanting to test locally.

Ideally we find something like rust-script which allows embedding dependencies into the script file.
In lieu of that, a comment at the top with how to set up the dependencies will suffice.