The goal here is to end up with a single "root" circuit representing any EVM proof. I.e. it must verify each STARK, but be general enough to work with any combination of STARK sizes (within some range of sizes that we chose to support). This root circuit can then be plugged into our aggregation circuit.
In particular, for each STARK, and for each initial `degree_bits` (within a range that we choose to support), this adds a "shrinking chain" of circuits. Such a chain shrinks a STARK proof from that initial `degree_bits` down to a constant, `THRESHOLD_DEGREE_BITS`.
The root circuit then combines these shrunk-to-constant proofs for each table. It's similar to `RecursiveAllProof::verify_circuit`; I adapted the code from there and I think we can remove it after. The main difference is that now instead of having one verification key per STARK, we have several possible VKs, one per initial `degree_bits`. We bake the list of possible VKs into the root circuit, and have the prover indicate the index of the VK they're actually using.
This also partially removes the default feature of CTLs. So far we've used filters instead of defaults. Until now it was easy to keep supporting defaults just in case, but here maintaining support would require some more work. E.g. we couldn't use `exp_u64` any more, since the size delta is now dynamic, it can't be hardcoded. If there are no concerns, I'll fully remove the feature after.
* First draft of 256-bit addition.
* Update comment.
* cargo fmt
* Rename addition evaluation file.
* Port ALU logic from SZ.
* Give a name to some magic numbers.
* `addition.rs` -> `add.rs`; fix carry propagation in add; impl sub.
* Clippy.
* Combine hi and lo parts of the output.
* Implement MUL.
* Suppress Clippy's attempt to make my code even harder to read.
* Next draft of MUL.
* Make all limbs (i.e. input and output) 16-bits.
* Tidying.
* Use iterators instead of building arrays.
* Documentation.
* Clippy is wrong; also cargo fmt.
* Un-refactor equality checking, since it was wrong for sub.
* Daniel comments.
* Daniel comments.
* Rename folder 'alu' -> 'arithmetic'.
* Rename file.
* Finish changing name ALU -> Arithmetic Unit.
* Finish removing dependency on array_zip feature.
* Remove operations that will be handled elsewhere.
* Rename var; tidy up.
* Clean up columns; mark places where range-checks need to be done.
* Import all names in 'columns' to reduce verbiage.
* cargo fmt
* Fix aux_in calculation in mul.
* Remove redundant 'allow's; more precise range-check size.
* Document functions.
* Document MUL instruction verification technique.
* Initial tests for ADD.
* Minor test fixes; add test for SUB.
* Fix bugs in generate functions.
* Fix SUB verification; refactor equality verification.
* cargo fmt
* Add test for MUL and fix some bugs.
* Update doc.
* Quiet incorrect clippy error.
* Clean up 'decode.rs'.
* Fold 'decode.rs' into 'arithmetic_stark.rs'.
* Force limb size to divide EVM register size.
* Document range-check warning and fix end value calc.
* Convert `debug_assert!`s into `assert!`s.
* Clean up various kinds of iterator usage.
* Remove unnecessary type spec.
* Document unexpected use of `collect`.
