class_docstr: Fusion in Decoder Agent with Rag Encoder swapped with ShiftInvariantRagEncoder.
code: def rag_model_type(self, model: str):
      self._rag_model_type = model
      self._rag_model_interface = Fid(self.opt, self.NULL_IDX)
  
imports: import torch
  import torch.nn
  import torch.cuda
  from typing import Optional, Union, Type
  from parlai.core.dict import DictionaryAgent
  from parlai.core.opt import Opt
  from parlai.core.params import ParlaiParser
  from parlai.agents.fid.fid import Fid, FidModel, T5FidModel
  from parlai.agents.rag.rag import RagAgent, T5RagAgent, BartRagAgent, TransformerGeneratorRagAgent, RagModelInterface
  from parlai.agents.rag.modules import RagModel, RagEncoder
  from .long_tga import TransformerVariantAgent, ShiftInvariantForwardEmbeddingMixin
label_desc: Use image node_id 2 for calling the LongFidAgent obj's underlying member method code with example usage: obj.rag_model_type(model) without return types