* Treat (the digest of) `cf_U_i1` as an additional public input to `AugmentedFCircuit` for full soundness

* Fix the y-coordinate in the affine form of zero points

This in turn fixes the inconsistency between the digest of a constant affine point and that of a witness affine point in circuits.

* Set `cf_u_i1_x` to the correct value

* Fix the number of public inputs in dummy instance and witness

* Unify the logic behind `CycleFoldCommittedInstanceVar::hash` and `CycleFoldChallengeGadget::get_challenge_gadget`

* Add `ToConstraintFieldGadget` bound to `GC2`

* Remove unnecessary code used for debugging

* Make clippy and rustfmt happy

* Move conversion methods for `NonNativeFieldVar` to `folding/circuits/nonnative.rs`

* Simplify the check of zero coordinates

* Gracefully handle the result of `nonnative_field_var_to_constraint_field`

* Make clippy happy again