fix(aztec.js): honor fee payment method in BatchCall.simulate

[Thunkar]

Summary

BatchCall.simulate() silently discarded options.fee.paymentMethod and dropped the merged payload's feePayer, so batches simulated with a sponsored/deferred fee method ran with the wallet's fallback handling (PREEXISTING_FEE_JUICE) instead of the caller's method. The wallet's account entrypoint then self-elected as fee payer and ended setup up front — a different phase structure than the caller asked for.

Resolves F-785. Surfaced while landing #24479.

Changes

• batch_call.ts: fetch options.fee.paymentMethod.getExecutionPayload(), merge it ahead of the batch (mirroring request()), and preserve combinedPayload.feePayer when rebuilding the ExecutionPayload.
• The wallet-side app-call offset only counts the wallet's own fee payment method, not one supplied via options.fee. So each batched call's private/public return-value index is offset by the fee payload's own call counts of each type; otherwise a call-contributing method (e.g. SponsoredFeePaymentMethod) shifts the indices and the fee call's return values decode as the first app call's.
• contract_function_interaction.ts: fixed the same latent off-by-one under a call-contributing fee method. The single app call is the last of its type in the payload, so its index is derived from the merged payload (avoiding a second getExecutionPayload() call).
• phase_check.parallel.test.ts: reverted the feat: assert non revertible phase when setting fee payer #24479 workaround back to the plain batch.simulate({ from, fee }) form now that the option is honored.

Testing

• Added 3 batch_call unit tests: return-value index offset (asserting on actual decoded values, not just absence of errors), feePayer from the payment method, and feePayer carried by a batched payload. Verified red/green — the offset test fails without the fix.
• All 3 phase_check e2e tests pass, including the reverted late-election test.
• No behavior change for batches simulated without fee.paymentMethod (offsets are 0).