getOrFallback method
Gets the stored value or returns a fallback if the value is null.
This is a convenience method that combines get() with a null check.
Example:
final coins = PrfInt('coins');
final value = await coins.getOrFallback(0); // Returns 0 if not set
Implementation
Future<T> getOrFallback(T fallback) async {
return (await get()) ?? fallback;
}