docstr: Train the agent in the environment and return the mean reward.
code: def train(
      self,
      n_steps: int = None,
      n_episodes: int = 10000,
      save_every: int = None,
      save_path: str = None,
      callback: callable = None,
      **kwargs,
  ) -> float:
      """Train the agent in the environment and return the mean reward."""
      raise NotImplementedError()
  
file_path: tensortrade/tensortrade/agents/agent.py
imports: from deprecated import deprecated
  import numpy
  from abc import ABCMeta, abstractmethod
  from tensortrade.core import Identifiable
label_desc: Use image node_id 4 for calling the Agent obj's underlying member method code with example usage: obj.train(n_steps, n_episodes, save_every, save_path, callback) without return types