fix(aztec-node): throw on existing nullifier in getLowNullifierMembershipWitness#21472

PhilWindle merged 2 commits intomerge-train/fairiesAztecProtocol/aztec-packages:merge-train/fairiesfrom

be/fix-low-nullifier-witness-errorAztecProtocol/aztec-packages:be/fix-low-nullifier-witness-errorCopy head branch name to clipboard