@std/async/unstable_wait_for.ts has flaky test

[BlackAsLight]

https://github.com/denoland/std/actions/runs/13148004852/job/36690141694

ERRORS 

waitFor() throws DOMException on timeout => ./async/unstable_wait_for_test.ts:16:6
error: AssertionError: Expected actual: "112" to be close to "100": delta "12" is greater than "10".
  throw new AssertionError(
        ^
    at assertAlmostEquals (file:///Users/runner/work/std/std/assert/almost_equals.ts:51:9)
    at file:///Users/runner/work/std/std/async/unstable_wait_for_test.ts:25:3

 FAILURES 

waitFor() throws DOMException on timeout => ./async/unstable_wait_for_test.ts:16:6

FAILED | 3099 passed (2720 steps) | 1 failed | 11 ignored (1m9s)

error: Test failed
Error: Process completed with exit code 1.

std/async/unstable_wait_for_test.ts

Lines 16 to 28 in 3b75ee7

	Deno.test("waitFor() throws DOMException on timeout", async () => {
	let flag = false;
	const id = setTimeout(() => flag = true, 1000);
	const start = Date.now();
	const error = await assertRejects(
	() => waitFor(() => flag === true, 100),
	DOMException,
	"Signal timed out.",
	);
	assertAlmostEquals(Date.now() - start, 100, 10);
	assertEquals(error.name, "TimeoutError");
	clearTimeout(id);
	});

[kt3k]

Maybe let's use FakeTime to simulate the timers. That should remove flakiness caused by timer's timings