Add support for progress indicators to pipelines

[tennlee]

It would be really neat to be able to set progress=True in the pipeline constructor, and have it print out some progress indicator based on the iterator specified. I'm not sure whether this should be simple prints of percent, or a fancy task bar like tqdm or Rich, but it would be quite nice for being able to see the rate and degree of progress during pipeline iteration.

[tennlee]

I think this should be a default, actually. There will be cases (like pipelines-of-pipelines) where you don't necessarily want them all reporting over the top of eachother, but it's probably fine to expect the user to turn these off in due course.