scopedWritable<T> static method
Returns a ReadableBeacon and a function that allows writing to the beacon.
This is useful for creating a beacon that's readable by the public,
but writable only by the owner.
Example:
var (count,setCount) = Beacon.scopedWritable(15);
Implementation
static (ReadableBeacon<T>, void Function(T)) scopedWritable<T>(
T initialValue) {
final beacon = WritableBeacon<T>(initialValue);
return (beacon, beacon.set);
}