feat: fastForwardContractUpdate cheatcode for simulating contract updates

[dbanks12]

Adds fastForwardContractUpdate to aztec.js — a high-level cheatcode that returns a SimulationOverrides blob simulating a deployed instance as if it had already been upgraded to a new contract class.

The blob covers both pieces required for a coherent upgrade simulation:

• overrides.publicStorage rewrites the ContractInstanceRegistry's delayed-public-mutable storage so the AVM's UpdateCheck resolves to the new class id.
• overrides.contracts swaps the deployed instance for one whose currentContractClassId is bumped to the new class. Drives both AVM-side public dispatch and PXE-side ACIR private dispatch.

Both pieces are required: a storage-only override would not redirect the AVM's class dispatch (which reads currentContractClassId from the contract DB); an instance-only override would cause the witgen UpdateCheck to throw on inconsistency. The new class must already be registered on chain.

import { fastForwardContractUpdate } from '@aztec/aztec.js';

const overrides = await fastForwardContractUpdate({ instanceAddress, newClassId, node });
const result = await contract.methods.upgraded_method().simulate({ overrides });

Test plan

• Unit tests in fastforward_contract_update.test.ts cover validation and override shape.
• E2E coverage in e2e_contract_updates for both public and private dispatch under override (private dispatch needs wallet.registerContractClass from upstack and the sync-skip narrowing from upstack).
• migration_notes.md and how_to_test.md updated.

[dbanks12]

• refactor(stdlib): consolidate find-function-by-selector helpers #23008
• feat: fastForwardContractUpdate cheatcode for simulating contract updates #22905 👈 (View in Graphite)
• feat(pxe,nr): flesh out account stubs and don't exclude syncing for overrides #23054
• feat: expose wallet.registerContractClass (prep for simulating contract upgrades) #22932 : 3 other dependent PRs (#22833 , #23016 , #23045 )
• feat: public data tree overrides for simulation #22830
• refactor: drop artifact field from SimulationOverrides #22957
• merge-train/fairies

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[Thunkar]

Nice!