class_docstr: Encodes numpy ndarray with compression into a spark dataframe field
code: def decode(self, unischema_field, value):
      memfile = BytesIO(value)
      return np.load(memfile)["arr"]
  
imports: from abc import abstractmethod
  from io import BytesIO
  import numpy
label_desc: Use image node_id 2 for calling the CompressedNdarrayCodec obj's underlying member method code with example usage: obj.decode(unischema_field, value) and returns: np