Circuit size field discrepancy in ECCVM recursive verifier

[ledwards2225]

The circuit size (required as a witness FF in the ZM recursive verifier) cannot be extracted from the transcript as an FF (bigfield) in the ECCVM recursive verifier. It is thus extracted as a BF and converted to an FF. Resolution may be an update to the transcript functionality or a change in the input type in ZM to match the builder FF.