feat(SourceT): add fromConsumableActionStep that creates a StepT from…

[giulioforesto]

… an action that consumes some data

Closes #1448

[giulioforesto]

This seems ready to land, modulo the hardest part: the name of your function :-)

I think I'm warming up to unfoldStep.

Haha go for unfoldStep then. I trust you, I don't master all the subtleties of Haskell function naming yet ;)

[giulioforesto]

There you go, thanks for the review

[ysangkok]

@giulioforesto The doctest isn't passing for me. Was this only meant as a hint/suggestion, or was it supposed to be actually be an executable doctest?