save method
Implementation
@override
Future<void> save(Wallet item) async {
final wallets =
(jsonDecode(await secureStorage.read(key: StorageKeys.wallets) ?? '[]')
as List<dynamic>)
.map((e) => Wallet.fromJson(e as Map<String, dynamic>))
.toList();
wallets.add(item);
secureStorage.write(key: StorageKeys.wallets, value: jsonEncode(wallets));
}