remember<T> static method
Retrieves an item, or stores the result of the callback if it doesn't exist.
Implementation
static Future<T> remember<T>(String key, Duration ttl, FutureOr<T> Function() callback) async {
final value = await get<T>(key);
if (value != null) return value;
final result = await callback();
await put(key, result, ttl: ttl);
return result;
}