Changes many fields to required -- as far as we were able to figure out,
signing would fail if these fields aren't provided anyway, so this
should not pose a compatibility problem.
Co-authored-by: matejcik <ja@matejcik.cz>
A change introduced in mypy 0.770 disallows overriding some system
modules, including `sys`.
We only need the override for `sys.print_exception`, and the simplest
solution is to make mypy ignore that particular call.
