use a shared prefences singleton for local storage

[pappes]

useful for key value pairs stored on the local device

import 'package:shared_preferences/shared_preferences.dart';

class PrefsSingleton { factory PrefsSingleton() { return _singleton; }

PrefsSingleton._internal();

static final PrefsSingleton _singleton = PrefsSingleton._internal();

static SharedPreferences? prefs; }