Use dataclass_transform decorator (typing_extensions)

[PierreRaybaut]

https://typing-extensions.readthedocs.io/en/latest/index.html#decorators

This could be useful to add typing hints for guidata.dataset.DataSet objects.

It would require to add a dependency over typing_extensions since the feature was introduced in standard typing package with Python 3.11 (and guidata still supports Python 3.9-3.10).