Allow For nodes to skip returning the inputs #674
Description
Inspired by @pmrv's comment: #603 (comment)
In general one needs to return the for-node inputs alongside its outputs in order to guarantee that they stay providentially coupled. However, for simple cases (e.g. a single, non-zipped/non-nested loop), it is unambiguous what the coupling is. Or maybe the user just wants to 100% promise that they either don't care or will take care of tracking this themselves. In all these cases, it would be nice to optionally turn off the inputs-in-the-output.