class_docstr: Average the scores of the true class by label
code: def __init__(self):
      self.label2mean: Dict[int, Mean] = defaultdict(Mean)
      self.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 1 to create a new MeanScores object from inherited base classes: Metric, ABC with example: obj = MeanScores()