fix: correct various issues with gym v21 compatibility env & update CI to work

[Trenza1ore]

Description

1. Improve Gym v21 protocol correctness (gym.Env.seed returns list[int] | None)
2. Call super().reset(seed=seed) in Gym v21 reset
3. Fix various issues with unit tests & CI

Fixes #147

Also opened this PR in upstream project dm_control:

• fix: use reshape instead of raw shape assignment for numpy arrays google-deepmind/dm_control#539

Type of change

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

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