fix(expect): race slow async poll fn against timeout deadline

[Anas0709]

Summary

Closes #9844

When the expect.poll callback is a slow async function, await fn() blocks for the full duration of fn regardless of the configured timeout. The timeout flag fired correctly but could not interrupt the in-flight await, so tests took orders of magnitude longer than expected (or hung until the global test timeout).

Root cause: the poll loop did await fn() unconditionally — no race against the deadline.

Fix: create a deadline Promise that rejects when the timeout fires and use Promise.race([fn(), deadlinePromise]) on non-last-attempt iterations. The last attempt still awaits fn() directly to preserve the existing "one final chance" semantics (_isLastPollAttempt). When the deadline wins, the last recorded assertion error (if any) is surfaced with the expected cause message so output is consistent with the normal timeout path.

Behaviour before / after

// fn takes 1000 ms, timeout is 100 ms
test('why 2000', async () => {
  await expect.poll(
    async () => { await new Promise(r => setTimeout(r, 1000)) },
    { timeout: 100 },
  ).toBe(1)
})

	Before	After
why 2000	fails after ~2075 ms	fails after ~100 ms ✅
stuck (fn: 10 s)	hangs until 5 s test timeout	fails after ~100 ms ✅
existing fast-fn tests	✅	✅
should handle success on last attempt	✅	✅ (last-chance preserved)

Test plan

• Added slow async fn is interrupted when timeout expires — asserts the test fails in < 1 s with "Matcher did not succeed in time."
• Added slow async fn timeout surfaces last assertion error when available — asserts the last assertion message is preserved when fn slows down after the first fast call
• All existing expect-poll tests still pass across threads, vmThreads, and forks pools

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