* Replace `CrandallQuarticField` with a more generic `QuarticExtension`
And likewise for `CrandallQuadraticField`.
There are a few parameters which we can't automatically derive (in const Rust), so I specified them in a `AutoExtendable` trait.
This would make it fairly easy to add extension fields for `GoldilocksField` and any future fields.
* Attempt to derive 2-adicity, see Hamish's feedback
* Simplify TWO_ADICITY based on chat with Hamish
* PR feedback
* Merge AutoExtendable into Extendable (#235)
* Move some Field members to a Field64 subtrait
I.e. move anything specific to 64-bit fields.
Also, relatedly,
- Tweak a bunch of prover code to require `Field64`, since 64-bit stuff is used in a couple places, like the FRI proof-of-work
- Remove `bits()`, which was unused and assumed a 64-bit field
- Rename a couple methods to reflect that they're u64 variants
There are no functional changes.
* Field64 -> PrimeField
* Remove `exp_u32`, `kth_root_u32`
* PrimeField: PrimeField
* Move `to_canonical_biguint` as well
* Add back from_noncanonical_u128
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).
My recent change made `padded` panic if the padded length is less than the current length. I figured that might indicate that something unexpected was going on, so might be good to fail fast.
It looks like `inv_mod_xn` was relying on the old `padded` behavior, and it seems correct AFAIK, i.e. in this case it wasn't a symptom of anything going wrong.
We could also restore the old behavior of `padded` if you prefer; let me know if you have a preferennce.
