fix(aztec-nr): update aes128 test mock for renamed batched shared_secrets oracle

[AztecBot]

Summary

PR #23352 (feat!: make get_shared_secrets batched oracle call) renamed the shared-secret oracle from aztec_utl_getSharedSecret (singular) to a batched aztec_utl_getSharedSecrets (plural) that returns a slot to an EphemeralArray<Field> of results. All production call sites were updated, but one stale mock in aes128.nr was missed, which broke the messages::encryption::aes128::test::encrypt_decrypt_deterministic test on merge-train/fairies CI.

Failure

• CI log: http://ci.aztec-labs.com/1779124738049879
• Failing test log: http://ci.aztec-labs.com/c92bb9ea62f25d91
• Error: No public key registered for address 0x25af…be70c. Because the test mocked the now-defunct oracle name, the real aztec_utl_getSharedSecrets oracle ran against the hard-coded recipient address, which is not registered as an account.

Fix

Update the test mock to match the new batched oracle's contract: push s_app into an EphemeralArray<Field> at a slot, then mock aztec_utl_getSharedSecrets to return that slot. This mirrors the mock_get_shared_secrets helper in oracle/shared_secret.nr added in #23352.

Full analysis: https://gist.github.com/AztecBot/da9da98fa2a3f10c8ff01fbaafa76995

ClaudeBox log: https://claudebox.work/s/827cef6e916dd72c?run=1

[AztecBot]

Automatically closing this stale claudebox draft PR (no updates for 5+ days). Re-open if still needed.