fix the rendering bug of MPE environment

[xixinzhang]

Description

• Bug Description: When using the following example code of environment simple_adversary_v3 as provided in the PettingZoo Doc, the rendering window disappears in a flash.

  from pettingzoo.mpe import simple_adversary_v3
  
  env = simple_adversary_v3.parallel_env(render_mode="human")
  observations, infos = env.reset()
  
  while env.agents:
      # this is where you would insert your policy
      actions = {agent: env.action_space(agent).sample() for agent in env.agents}
  
      observations, rewards, terminations, truncations, infos = env.step(actions)
  env.close()

• Bug location: In file pettingzoo/mpe/_mpe_utils/simple_env.py
  The variable "render_fps": 10 in line 34 is not used to control the rendering speed.

Type of change

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• Bug fix (non-breaking change which fixes an issue)

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Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have run pytest -v and no errors are present.
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I solved any possible warnings that pytest -v has generated that are related to my code to the best of my knowledge.
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[elliottower]

Thanks for catching this, going to check the other MPE environments right now to make sure there's nothing else that has this issue. I went through the other non-MPE environments a little while back to fix this but I wasn't familiar with MPE (and it is being moved to a separate repo, MPE2 in the future)

[elliottower]

Okay yeah this looks good, I see it's a helper util for all the MPE envs.