multicallBalanceOf method
Multicall of balanceOf, may not be in the same block.
Implementation
Future<List<BigInt>> multicallBalanceOf(List<String> addresses) async {
assert(addresses.isNotEmpty, 'address should not be empty');
return Future.wait(Iterable<int>.generate(addresses.length)
.map((e) => balanceOf(addresses[e])));
}