feat: support for multiple vscales per run

[regehr]

so the basic approach here is to check if src or tgt actually uses vscale, and if not to behave as before. if so, we use the typechecker to enumerate vscale values.
I'm not in love with the code, I think it works but I think doing this through the solver isn't any better than just enumerating in C++, or is there a way I should be doing this better?

[nunoplopes]

I really don't like this approach, sorry.
Why is it not using the type inference mechanism? It's much simpler.
See the IntType::getTypeConstraints & IntType::fixup. That's all you need changing (for AggregateType).