Bug fixes regarding intersection env & enhancements regarding community contributions

HighwayEnv v1.12.1

This is a minor bug fix + maintenance release, mainly affecting the intersection environment and its variants.

Bug fix

• Prevent in-loop list mutation & removing controlled vehicles in rare cases by @Trenza1ore & @AntaresFeng (#721)
• Validate nested config dicts in default_config override for all envs & fix default config for variants of intersection env by @Trenza1ore & @AntaresFeng (#724)
• Prevent uint8 overflow of OccupancyGrid observation shape by @teddytennant & @Trenza1ore (#709)

Documentation

• Fixed documentation website's edit button by @Trenza1ore (#708)
• Use the new celshast package for documentation theme by @Trenza1ore (#719)

Community

• Initial version of our AI policy for contribution by @Trenza1ore (#714)
• Ensure the appropriate line ending is enforced w/ .gitattributes & pre-commit by @Trenza1ore (#717)

CI and build

• Update license and use PEP 639 license declaration in pyproject.toml by @Trenza1ore (#718)
• Extend CI to cover macOS & Windows by @Trenza1ore (#725)
• General CI improvements by @mwydmuch (#710, #712)

Others

• Specify docstring convention for HighwayEnv to be pep257 & minor linting improvements by @Trenza1ore (#722)

New Contributors

• @teddytennant made their first contribution in #709
• @AntaresFeng made their first contribution in #721

Full Changelog: v1.12...v1.12.1