No functional changes here. The biggest change was moving certain files into new directories like `plonk` and `iop` (for things like `Challenger` that could be used in STARKs or other IOPs). I also split a few files, renames, etc, but again nothing functional, so I don't think a careful review is necessary (just a sanity check).
* Make ZK optional
* Remove rate from FriConfig
Seems redundant, and we've had some tests break due to the two fields not matching.
* zero_knowledge: false in bench