Rename minigrid.py to minigrid_env.py

[rodrigodelazcano]

Description

Due to import errors because the package name was the same as a root file mujoco.py (#243), this PR renames the mujoco.py file to mujoco_env.py.

This PR also reverts the changes of moving manual_control.py and benchmark.py to a new directory examples, since it's no longer required. #244

Type of change

Please delete options that are not relevant.

• [x] 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

Screenshots

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Checklist:

• [x] 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
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes