checkBalance method
Implementation
Future<BigInt> checkBalance(String address, { String? coinType }) async {
coinType ??= AptosClient.APTOS_COIN;
String typeTag = "0x1::coin::CoinStore<$coinType>";
final accountResource = await aptosClient.getAccountResource(address, typeTag);
return BigInt.parse(accountResource["data"]["coin"]["value"]);
}