zope.interface uses class magic to define interfaces. Mypy doesn't
like the methods without arguments and raises a warning for the
dozens of them in repository.py.
This commit adds type annotation comments to silence the error.
TBH I'm not sure if this is the best way to do this. But it does
get the job done. We may have to revisit once we add proper type
annotations to this file. For now, it makes mypy's output far
less verbose.