Extract utility functions and types to separate module and repo

[zerebubuth]

@rmarianski writes in a comment:

I wonder if we should at some point just create our own repo to hold these kinds of objects and related utility functions?

Yup! Although it's hard to know where the line is sometimes, since we don't want to have to make "cross-cutting" changes to interfaces across several repos at the same time. However, I think there's a core of useful stuff that doesn't change much and we can reuse.