code: def save_checkpoint(self, checkpoint_dir):
      path = os.path.join(checkpoint_dir, "checkpoint")
      with open(path, "wb") as outputFile:
          pickle.dump(
              (self.config, self.nthread, self.model.save_raw()),
              outputFile,
          )
  
imports: from typing import Dict, Any, Optional, TYPE_CHECKING
  import sklearn.datasets
  import sklearn.metrics
  import os
  from sklearn.model_selection import train_test_split
  import xgboost
  from xgboost.core import Booster
  import pickle
  import ray
  from ray import train, tune
  from ray.tune.schedulers import ResourceChangingScheduler, ASHAScheduler
  from ray.tune import Trainable
  from ray.tune.execution.placement_groups import PlacementGroupFactory
  from ray.tune.experiment import Trial
  from ray.tune.integration.xgboost import TuneReportCheckpointCallback
label_desc: Use image node_id 3 for calling the BreastCancerTrainable obj's underlying member method code with example usage: obj.save_checkpoint(checkpoint_dir) without return types