Vehicle behaviour fix, generic merge env, Gymnasium-compliant render behaviour, and docs refresh

HighwayEnv v1.12.0

This is a big release that brings:

• a new generic version of the merge environment
• major documentation updates
• reduction in startup latency
• improvements in dependency situation (replacing pygame with pygame-ce, removing scipy)
• multiple new environment versions due to a bug discovered in neighbouring vehicle detection in environments with multiple road segments (causing non-player vehicles to have a higher likelihood of crashing than they should, as shown here).

Minor breaking change

Previously, HighwayEnv did not implement render mode according to Gymnasium; instead, whether the environments are actually rendered is set with the offscreen_rendering config key. #700 introduced correct behaviour for treating different values of render_mode, while still keeping old config keys as overrides:

• render_mode="human" -> render to window by default, render() returns None
• render_mode="rgb_array" -> headless render by default, render() returns image array
• Keeping offscreen_rendering in config as an override
• The OFFSCREEN_RENDERING environment variable is now ignored because explicit is better than implicit

So, basically, you can set render_mode="rgb_array" and pass offscreen_rendering=True in the config dict to get both an RGB array returned by render() and pygame rendering in a new window for your viewing pleasure (note that you still need real_time_rendering=True to render at the intended fps).

New environment variant

• Generic version of the merge environment (merge-generic-v0, merge-generic-v1) by @Minipoloalex (#694)

New environment version

• With neighbour vehicle detection fix: exit-v1, intersection-v2, intersection-multi-agent-v2, merge-v1, racetrack-v1, racetrack-large-v1, racetrack-oval-v1, roundabout-v1, roundabout-generic-v1, u-turn-v1 by @Lidang-Jiang (#667)

Bug fix

• Fix neighbour_vehicles not detecting vehicles on connected lanes by @Lidang-Jiang (#667)
• Ensure compliance with Gymnasium's definition of render_mode by @Trenza1ore (#700)
• Minor typing and NumPy 2.x compatibility fixes by @Trenza1ore (#698, #705)
• Call super in LinearVehicle.randomize_behavior by @m-walters (#614)

Dependencies

• Replaced pygame with pygame-ce by @Trenza1ore (#678)
• Removed dependency on scipy by @Trenza1ore (#691)

Performance

• Reduced startup latency by initializing only the needed pygame modules by @Trenza1ore (#687)

Documentation

• Docs added for 4 existing environments (exit, lane_keeping, two_way, u_turn) by @Trenza1ore (#697)
• Docs added for rendering modes and configurations by @Trenza1ore (#700)
• Docs added for neighbour vehicle detection issue by @Trenza1ore & @Lidang-Jiang (#667)
• Release notes section by @Trenza1ore (#706)
• Update outdated sections in docs by @Trenza1ore (#699)
• Fixed warnings in documentation build process by @Luzijano & @Trenza1ore (#690, #695)

Community

• Readme rewritten for compactness by @kydrahul & @Trenza1ore (#682)
• Contributing guideline written by @kydrahul & @Trenza1ore (#702)
• Issue & pull request templates by @Trenza1ore (#679)
• Unit test coverage requirements for pull requests by @Trenza1ore (#705, #707)

CI and build

• General CI improvements by @mwydmuch & @Trenza1ore (#680, #681, #683)

New Contributors

• @Trenza1ore made their first contribution in #678
• @mwydmuch made their first contribution in #680
• @kydrahul made their first contribution in #682
• @Luzijano made their first contribution in #690

Full Changelog: v1.11...v1.12