feature: readline-like functionality for interactive scenario test

[ecioppettini]

Really low priority, especially because I'm not sure if someone actually uses it, but I've been playing with the interactive scenario test and I think it's a cool thing. I think it would be cooler if you could use arrow keys to get the history, though, (maybe even completion?).

Maybe we could add rustyline?

Or maybe controlling it externally from a terminal would be simpler?