fix(aztec-nr): update aes128 encrypt_decrypt_deterministic mock for batched shared-secrets oracle

[AztecBot]

Summary

messages::encryption::aes128::test::encrypt_decrypt_deterministic started failing on merge-train/fairies with:

No public key registered for address 0x25afb798ea6d0b8c1618e50fdeafa463059415013d3b7c75d46abf5e242be70c.

(CI log: http://ci.aztec-labs.com/1779180119205688 — test log http://ci.aztec-labs.com/a175e0d0d44ab60f)

Cause

PR #23352 (feat!: make get_shared_secrets batched oracle call) renamed aztec_utl_getSharedSecret → aztec_utl_getSharedSecrets (plural) and changed the return contract: the oracle now returns a Field slot pointing at an EphemeralArray<Field> of per-key shared secrets, rather than returning the secret value directly.

The encrypt_decrypt_deterministic test in noir-projects/aztec-nr/aztec/src/messages/encryption/aes128.nr was still mocking the old singular oracle name with OracleMock::mock("aztec_utl_getSharedSecret").returns(s_app). The new oracle is unmocked, so when AES128::decrypt calls get_shared_secret(..) (which now wraps get_shared_secrets), TXE falls through to its real implementation and rejects the hard-coded test recipient that has no registered public key.

Fix

Mirror the pattern used by the new tests in oracle/shared_secret.nr (mock_get_shared_secrets): push s_app into an EphemeralArray<Field> at a known slot and mock aztec_utl_getSharedSecrets to return that slot.

Verification

• nargo check --deny-warnings on noir-projects/aztec-nr passes after the change.
• Full test run requires TXE (yarn-project), validated by CI on this PR.

ClaudeBox log: https://claudebox.work/s/45bbfbcfde746737?run=1