effect function
Runs a reactive side-effect callback cb whenever any accessed signal changes.
Returns a disposer function that cancels future executions of the effect.
Example:
final count = signal(0);
final dispose = effect(() {
print('Count is now: ${count.value}');
});
count.value = 1; // prints "Count is now: 1"
dispose(); // Stops the effect
Implementation
void Function() effect(void Function() cb, {String? debugLabel}) {
return sf.effect(cb, debugLabel: debugLabel);
}