class_docstr: Adds a dummy channel to an image, also known as expanding an axis or unsqueezing a dim
  This will make an image of size (28, 28) to now be
  of size (1, 28, 28), for example.
  
  param axis: (int): dimension to be expanded to singleton
code: def __call__(self, *inputs):
      outputs = []
      idx = None
      for idx, _input in enumerate(inputs):
          _input = _input.unsqueeze(self.axis)
          outputs.append(_input)
      return outputs if idx >= 1 else outputs[0]
  
imports: import os
  import random
  import math
  import numpy
  import torch
label_desc: Use image node_id 2 for calling the AddChannel obj's underlying member method code with example usage: obj.__call__() and returns: unknown