Feat: Nullifying Proofs on Server

[jp4g]

Emitting a nullifier prevents proofs from using the nullifiers. Should:

• Emitting a nulllifier should delete all proofs that contain that nullifier

• Incoming degree proofs should check to see if any contained nullifiers are already emitted

  Todo out of scope:

  • Ensure nullified relationships don't show for users
  • Show pending half-nullified relationships, maybe do automatically?