Calculate class_commitment from proof

[notlesh]

This works around an issue introduced when Pathfinder removed class_commitment from its class proof.

Any proof starts with the root node, and hashing that root node gives the Merkle root of that tree. class_commitment is really just the Merkle root of the class tree, so this is all we need to reconstruct it.

Note, however, that this is redundant -- verify_proof() ultimately hashes the root node and compares that to class_commitment, which is exactly what this PR does. It would be just as good to make class_commitment an Option an only verify it then; but this PR at least makes the problem clear.

Type

• feature
• bugfix
• dev (no functional changes, no API changes)
• fmt (formatting, renaming)
• build
• docs
• testing

Description

Breaking changes?

• yes
• no