Torchgfn

Bug fix : https://github.com/saleml/torchgfn/issues/134
+ From now on, the published version (on pypi) and the release should correspond to the `stable` branch

Minor API changes from v1 - for simplicity.

Major API change. More flexibility in environment creation.

This version incudes all the functionalities used in other codebases that rely on this library up to this day.

With the given code, results published in several papers can be reproduced.

This should be the last version before v1, that supports more generic environments.

In this version, the name of the repo (as well as the pypi package and the docs) has changed to `torchgfn`.

This version supports simple discrete environments, and is used in published research papers.