Scoru,Proto: polish `Proof_repr`

Context

Found a little window to refactor a bit the code, others mr should come. This mr should not change the semantic of the refutation's mechanism. If so, please call me names.

Manually testing the MR

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Checklist

• n/a Document the interface of any function added or modified (see the coding guidelines)
• n/a Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• n/a For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR