Folding + IVC for Add Circuit

[volhovm]

We have a circuit for Add, we have IVC, but these two need to be concatenated properly.

This task can be closed when:

• IVC + Add circuit are concatenated and folded properly
• The combined witness satisfies the combined expression
• We can pass the combined instance into (a variant) of plonkish prover (to be implemented within this task)
• This prover succeeds and veriifes (completeness test)