class_docstr: Metadata describing serialized sample in a memory buffer.
  
  It is passed through memory, stored after sample it describes.
code: def __init__(self, offset, shape, dtype, nbytes):
      self.shape = shape
      self.dtype = dtype
      self.offset = offset
      self.nbytes = nbytes
  
imports: import os
  from nvidia.dali._multiproc import shared_mem
  from nvidia.dali._multiproc.messages import ShmMessageDesc
  from nvidia.dali._utils.external_source_impl import assert_cpu_sample_data_type, sample_to_numpy
  import pickle
label_desc: Use image node_id 1 to create a new SampleMeta object  with example: obj = SampleMeta(offset, shape, dtype, nbytes)