fix: flaky test due to overflow ub

[c8ef]

Why

Fixes #461.

The duration cast here with max seconds is UB.

async_simple/async_simple/coro/Sleep.h

Lines 36 to 42 in 8df816f

	Lazy<void> sleep(Executor* ex, std::chrono::duration<Rep, Period> dur,
	uint64_t schedule_hint) {
	auto slot = co_await CurrentSlot{};
	co_await ex->after(std::chrono::duration_cast<Executor::Duration>(dur),
	schedule_hint, slot);
	}

Proof: https://godbolt.org/z/v878q1Yjf

What is changing

Change to a big enough value without overflow.

Example

[c8ef]

cc @ChuanqiXu9 @poor-circle

[poor-circle]

Thanks! This problem worry me a long time.

[poor-circle]

LGTM