= Embassy runtime

The Embassy excecutor is an async/await executor designed for embedded usage.

* No `alloc`, no heap needed. Task futures are statically allocated.
* No "fixed capacity" data structures, executor works with 1 or 1000 tasks without needing config/tuning.
* Integrated timer queue: sleeping is easy, just do `Timer::after(Duration::from_secs(1)).await;`.
* No busy-loop polling: CPU sleeps when there's no work to do, using interrupts or `WFE/SEV`.
* Efficient polling: a wake will only poll the woken task, not all of them.
* Fair: a task can't monopolize CPU time even if it's constantly being woken. All other tasks get a chance to run before a given task gets polled for the second time.
* Creating multiple executor instances is supported, to run tasks with multiple priority levels. This allows higher-priority tasks to preempt lower-priority tasks.