Migrating to gymnasium

[KelvinYang0320]

TODO:

• step
  • gymnasium.Env.step(self, action: ActType) → tuple[ObsType, SupportsFloat, bool, bool, dict[str, Any]]
  • Add is_terminated() and is_truncated() according to these lines.
• reset
  • gymnasium.Env.reset(self, *, seed: int | None = None, options: dict[str, Any] | None = None) → tuple[ObsType, dict[str, Any]]
  • Add **kwargs in reset() for the seed parameter
  • Return a tuple in reset() with {} according to this line.
• requirement.txt
  • Follow gymnasium version in SB3.
• code comments

Testing:

• Gymnasium Deepworlds deepworlds#101