ariaBusy and control timing for update

~~~js
export const count = num.u8()

/** @example html```
0
```
will set `aria-busy=true` for 3s until the value change
*/ export function increment() {
count.set(it => it + 1, { delay: 3*s })
}
~~~

#### Why make it builtin?
I'm thinking to make every accessibility feature be builtin into the framework. So this one is the first step towards that.