class_docstr: The abstract LM class
  
  To share the loss calculation way among different models,
  We uses delegate pattern here:
  The instance of this class should be passed to "LanguageModel"
  
  >>> from espnet2.lm.abs_model import AbsLM
  >>> lm = AbsLM()
  >>> model = LanguageESPnetModel(lm=lm)
  
  This "model" is one of mediator objects for "Task" class.
code: def forward(
      self, input: torch.Tensor, hidden: torch.Tensor
  ) -> Tuple[torch.Tensor, torch.Tensor]:
      raise NotImplementedError
  
file_path: espnet/espnet2/lm/abs_model.py
imports: from abc import ABC, abstractmethod
  from typing import Tuple
  import torch
  from espnet.nets.scorer_interface import BatchScorerInterface
label_desc: Use image node_id 1 for calling the AbsLM obj's underlying member method code with example usage: obj.forward(input, hidden) without return types