* Add a reduce_polys_base
Reducing the polynomials in `open_plonk` was taking ~100ms on my machine. It was converting BF polynomials to the EF early on; by doing more work in the BF we can reduce it to ~20ms.
* PR feedback
* Add a tree of scopes for proving times
To replace the old `timed!` macro, which had no hierarchy.
It's similar to `ContextTree`, which tracks gate counts of circuit operations.
This gives a more organized output, with indentation levels based on scope depth, parent durations listed before child durations, etc.
* PR feedback
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).
