class_docstr: Keep only the most recent turn.
  
  This mutator obliterates the history of the conversation, keeping only the very last
  thing said. Every turn is still evaluated, but treated as a new episode.
code: def add_cmdline_args(
      cls, parser: ParlaiParser, partial_opt: Optional[Opt] = None
  ) -> ParlaiParser:
      parser.add_argument(
          "--preserve-context",
          default=True,
          type="bool",
          help="If extra context is provided, keep it prepended to all turns.",
      )
  
file_path: ParlAI/parlai/mutators/last_turn.py
imports: from typing import List, Iterator, Optional
  from parlai.core.opt import Opt
  from parlai.core.params import ParlaiParser
  from parlai.core.message import Message
  from parlai.core.mutators import ManyEpisodeMutator, register_mutator
label_desc: Use image node_id 1 for calling the LastTurnMutator obj's underlying member method code with example usage: obj.add_cmdline_args(cls, parser, partial_opt) without return types