Reduce duplication in zk transcript classes

[ludamad]

To the extent we want to maintain these test/debugging-only classes, we should not be duplicating them between zk flavours

[ludamad]

Note as counter-point https://github.com/AztecProtocol/barretenberg/issues/877. I overall think this is a symptom of a bigger thing - our flavor pattern is a leaky pattern, with many special cases. I think we should look into just generating these.

[iakovenkos]

This transcript pattern also obstructs the sharing of transcripts among several provers. In CIVC prove(), we have a sequence of provers MegaZK -> Merge -> ECCVMProver -> Translator, where each Prover expects a Transcript of Flavor::Transcript type. Although we could, in theory, template provers and verifiers on Transcript or TranscriptParams, it feels nasty, especially considering the limited usability of serialize/deserialize_full_transcript methods.