Transfer tests from unittest to pytest

[pascal-roth]

Description

Started to transition tests from unittest to pytest and add new tests.

CURRENTLY NOT ALL TESTS ARE WORKING

TODO:

• test_contact_sensor need cleanup with definition of parameterizations to avoid for loops
• test_tiled_camera_env needs a long time -- is that intended

Fixes # (issue)

Type of change

• New feature (non-breaking change which adds functionality)

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• 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
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there