class_docstr: A feature concatenation block.
  
  :param in_keys: Keys identifying the input tensors.
  :param out_keys: Keys identifying the output tensors.
  :param in_shapes: List of input shapes.
  :param concat_dim: The index of the concatenation dimension.
code: def __repr__(self):
      txt = ConcatenationBlock.__name__
      txt += f"\n\tconcat_dim: {self.concat_dim}"
      txt += f"\n\tOut Shapes: {self.out_shapes()}"
      return txt
  
file_path: maze/maze/perception/blocks/general/concat.py
imports: from typing import Union, List, Dict, Sequence
  import torch
  from maze.core.annotations import override
  from maze.perception.blocks.base import PerceptionBlock
label_desc: Use image node_id 3 for calling the ConcatenationBlock obj's underlying member method code with example usage: obj.__repr__() and returns: txt