Implement CycleFold in Nova's IVC (#45)

* Implement CycleFold in Nova's IVC

(CycleFold: https://eprint.iacr.org/2023/1192)

* CycleFoldChallengeGadget: add points coordinates as bytes

* Apply PR review suggestions

src/constants.rs

@@ -1,3 +1,5 @@
-// used for committed instances hash, so when going to the other curve of the cycle it does not
-// overflow the scalar field
-pub const N_BITS_HASH: usize = 250;
+// used for the RO challenges.
+// From [Srinath Setty](research.microsoft.com/en-us/people/srinath/): In Nova, soundness error ≤
+// 2/|S|, where S is the subset of the field F from which the challenges are drawn. In this case,
+// we keep the size of S close to 2^128.
+pub const N_BITS_RO: usize = 128;