GitLab

Make sure the coverage reports are copied to CircleCI artifacts,
and report them in colored output in interactive terminals only.

This reverts commit c864ac4e.

This is with using mypy in "default checks" mode, i.e. via:

    mypy --check-untyped-defs

Further annotations will be added of course, strengthening type-safety
even more beyond the "defaults" identified with mypy type-inference.