Update to support Gymnasium v1.0

[pseudo-rnd-thoughts]

This PR works to update the project to Support Gymnasium v1.0

In part it adds testing using check_env for all the registered highway-env environments, which uncovered a couple of issues that are fixed (primarily in exit env and the multi-agent wrapper)

As a result of removing the plugin system requiring that users import highway_env to register the environments, I have bumped the project version to 2.0.0, this might be unnecessary and we could use 1.10.0

[LucasAlegre]

Looks good to me!

[eleurent]

LGTM too, thanks Mark!

[eleurent]

Since this was merged, the upload to PyPi is now failing (e.g. for release 1.10) with

ERROR InvalidDistribution: Metadata is missing required fields: Name.

see https://github.com/Farama-Foundation/HighwayEnv/actions/runs/10442911768/job/28915719241

Do you have an idea where this Name metadata should go, by any chance?

[pseudo-rnd-thoughts]

Since this was merged, the upload to PyPi is now failing (e.g. for release 1.10) with

ERROR InvalidDistribution: Metadata is missing required fields: Name.

see https://github.com/Farama-Foundation/HighwayEnv/actions/runs/10442911768/job/28915719241

Do you have an idea where this Name metadata should go, by any chance?

The problem is that the release is using setup.py to install rather than python -m build.
setup.py install has been deprecated so I made #615