gymnasium==1.0 support

[Kallinteris-Andreas]

Description

• Updates import to work without the removed plugin system (and updates the DOC)
• pin gymnasium==1.0.0a1
• update tests to not use the removed env.get_attr()
• fix bounds check string Fix mujoco_rendering.py Gymnasium#634
• relax MuJuCo version requirements
• added MazeEnv.model and MazeEnv.data properties (useful for testing)

Type of change

• Documentation only change (no code changed)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• 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

[Kallinteris-Andreas]

Only MaMuJoCo-v0 environments tests are failing, requesting an approval regardless since this will be replaced with MaMuJoCo-v1 with the other PR
@rodrigodelazcano