`StructureTest` should retrieve the proof from proof_data rather than calling `export_proof`

[maramihali]

Some of our provers call transcript->export_proof() in their export_proof while others return transcript->proof_data we should make this uniform, probably have all provers call transcript->export_proof() and then the StructureTest should operate directly on proof_data to avoid any unforseen side effects.

[iakovenkos]

Partly handled by AztecProtocol/aztec-packages#14144
Most of the provers return proof by exporting it from the transcript. Except for the case when HasIPAAccumulator<Flavor>==true