Fix tictactoe reset bug (when one agent died)

[Cheaple]

Description

In a tictactoe environment env, if env get resetted when an possible agent is not in the env.agents list (for invalid action or other reasons), that agent would not be selected forever, since env._agent_selector always gets re-initialized with the list env.agent which misses that agent. To fix this situation, env._agent_selector should get re-initialized with env.possible_agents (which contains all possible agents.) rather than env.agents.

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.
  • only Format YAML files. failed.
• 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.
  • there is an error, which also happens before my commit
• 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

[David-GERARD]

I had to close and reopen the PR to trigger the CI tests.

[benblack769]

Hi, can you post a particular set of inputs/calls which causes the failure case you found? The current code sets self.agents = self.possible_agents[:] at the beginning of the reset function, which means that all agents should be included after reset.

Additionally, this environment follows the same pattern as the chess https://github.com/Farama-Foundation/PettingZoo/blob/master/pettingzoo/classic/chess/chess.py#L241 environments. So I'm wondering what sort of inputs could cause the error mentioned.