class_docstr: Impala Network which also outputs penultimate representation layers.
code: def __call__(self, x):
      for stack in self._stacks:
          x = stack(x)
      return nn.relu(x)
  
imports: import itertools
  import time
  from typing import Optional, Sequence, Tuple, Union
  from absl import logging
  from dopamine.discrete_domains import atari_lib
  from flax import linen
  import gin
  import jax
  import jax.numpy
  import numpy
label_desc: Use image node_id 2 for calling the ImpalaEncoder obj's underlying member method code with example usage: obj.__call__(x) and returns: nn