Create second project for mypy-protobuf

[nipunn1313]

This was a rudimentary way of having multiple mypy commands per project (as needed here). It might be more elegant to have multiple mypy_cmd within a project, but it seemed nontrivial to achieve, and I was able to whip this mechanism up more quickly - using multiple projects with one mypy_cmd per project. Not the most proud of it, but it works.

[nipunn1313]

It's not super critical this gets in. If the implementation strategy gives you the eebie jeebies, I think it's ok for this to wait for a better impl.

[hauntsaninja]

Thanks, let me think about this one!