Fix flaky IAP flow test: spurious async and mock delays

[Copilot]

The IAP flow test suite was non-deterministic due to two compounding bugs that caused it to exceed tap's 30-second per-file timeout on slower CI machines.

Root causes

1. should_iap_transaction_history_be_refreshed incorrectly declared async

The function had no await inside it but was declared async, and its call site omitted await. This meant the guard check received a Promise (always truthy) instead of a boolean — so !should_iap_transaction_history_be_refreshed(account) was always false and the early-return never fired. Every GET /accounts/:pubkey call triggered a full Apple IAP refresh, even for active accounts that needed no refresh.

// Before — returns Promise, guard never fires
async function should_iap_transaction_history_be_refreshed(account) { … }

// After — returns boolean, guard works correctly
function should_iap_transaction_history_be_refreshed(account) { … }

2. Artificial 500ms delays in the mock IAP controller

getTransactionHistory and verifyAndDecodeTransaction each used setTimeout(…, 500). Combined with the always-refresh bug, every GET call added 500ms (fetch) + 500ms × N (decode), pushing the test file from ~3s to ~17s — near the timeout limit. The reject() calls also lacked a return, falling through to a subsequent resolve().

// Before
return new Promise((resolve, reject) => {
  setTimeout(() => {
    if (!this.mock_controller.mock_transaction_data[transactionId]) {
      reject(new APIException(400, 4000006))  // no return — falls through to resolve
    }
    resolve({ signedTransactions: …, hasMore: false })
  }, 500)
})

// After
if (!this.mock_controller.mock_transaction_data[transactionId]) {
  return Promise.reject(new APIException(400, 4000006))
}
return Promise.resolve({ signedTransactions: …, hasMore: false })

Impact

	Before	After
IAP flow test suite time	~17s	~3s
Full test suite time	~44s	~32s