disposeInstances method
Implementation
int disposeInstances(int? amountToRemove) {
  if (amountToRemove == null || amountToRemove < 1) return 0;
  var keys = List.from(_cacheInstances.keys);
  var removed = 0;
  for (var k in keys) {
    _cacheInstances.remove(k);
    removed++;
    if (removed >= amountToRemove) {
      return removed;
    }
  }
  return removed;
}