Replace `Waiter` with `hlt`

[saza-ku]

Now we use Waiter (https://github.com/mewz-project/mewz/blob/main/src/sync.zig#L36) to wait for interruption and data.

But we could replace it with simply hlt, because it stops until an interruption occurs.

To do so, we would avoid exclusion control and save CPU time of host.