- **Soundness fix:** `TimerQueue` did not wait long enough in `Duration` based delays. Fixing this sadly required adding a `const TICK_PERIOD` to the `Monotonic` trait, which requires updating all existing implementations.
- If the queue was non-empty and a new instant was added that was earlier than `head`, then the queue would no pend the monotonic handler. This would cause the new `head` to be dequeued at the wrong time.