Simplified system for extended tasks

[clefourrier]

Extended tasks are now included in the main lighteval code, though they will only be imported if dependencies are available.
Still need to find a way to provide all the tasks name somewhere, probably in the examples.

[clefourrier]

@NathanHB do you need anything else for a review? :)

[clefourrier]

Tests are failing because of a breaking change in huggingface_hub, which no longer has huggingface_hub.inference._text_generation.
@Wauplin would you advise up setting a lower or upper bound to your lib?

[Wauplin]

Tests are failing because of a breaking change in huggingface_hub, which no longer has huggingface_hub.inference._text_generation.
@Wauplin would you advise up setting a lower or upper bound to your lib?

Oopsi oopsi, sorry about that! 😬
I definitely advice to set a lower bound for huggingface_hub lib', otherwise you won't be able to upgrade anymore. I opened a PR to fix this: #129.

[NathanHB]

LGTM