base36ToDecimal function
Implementation
BigInt base36ToDecimal(String base36Number) {
  final base36Characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  BigInt decimalValue = BigInt.zero;
  for (int i = 0; i < base36Number.length; i++) {
    int digitValue = base36Characters.indexOf(base36Number[i]);
    decimalValue = decimalValue * BigInt.from(36) + BigInt.from(digitValue);
  }
  return decimalValue;
}