docstr: Return example trk file bytes and struct view onto bytes
code: def trk_with_bytes(self, trk_key="simple_trk_fname", endian="<"):
      """Return example trk file bytes and struct view onto bytes"""
      with open(DATA[trk_key], "rb") as fobj:
          trk_bytes = bytearray(fobj.read())
      dt = trk_module.header_2_dtype.newbyteorder(endian)
      trk_struct = np.ndarray((1,), dt, buffer=trk_bytes)
      trk_struct.flags.writeable = True
      return trk_struct, trk_bytes
  
imports: import copy
  import os
  import sys
  import unittest
  from io import BytesIO
  from os.path import join
  import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from ...testing import assert_arr_dict_equal, clear_and_catch_warnings, data_path, error_warnings
  from ..None import trk
  from ..header import Field
  from ..tractogram import Tractogram
  from ..tractogram_file import HeaderError, HeaderWarning
  from ..trk import TrkFile, decode_value_from_name, encode_value_in_name, get_affine_trackvis_to_rasmm
  from .test_tractogram import assert_tractogram_equal
label_desc: Use image node_id 4 for calling the TestTRK obj's underlying member method code with example usage: obj.trk_with_bytes(trk_key, endian) and returns: trk_struct,  trk_bytes