class_docstr: Base class for the plugins that show the scores of the true class, averaged
      by new and old classes.
  
  :param image_creator: The function to use to create an image of the history
      of the mean scores grouped by old and new classes
code: def reset(self) -> None:
      self.mean_scores.reset()
  
imports: from abc import ABC, abstractmethod
  from collections import defaultdict
  from typing import Callable, Dict, Set, TYPE_CHECKING, List, Optional, TypeVar
  import torch
  from matplotlib.axes import Axes
  from matplotlib.figure import Figure
  from matplotlib.pyplot import subplots
  from torch import Tensor, arange
  from avalanche.evaluation import Metric, PluginMetric
  from avalanche.evaluation.metric_utils import get_metric_name
  from avalanche.evaluation.metrics import Mean
  from avalanche.evaluation.metric_results import MetricValue, AlternativeValues
  from typing_extensions import Literal
label_desc: Use image node_id 2 for calling the MeanScoresPluginMetricABC obj's underlying member method code with example usage: obj.reset() without return types