Add a wikirace task

[phhusson]

This commits adds a 'wikirace" task, the idea is this:
You are currently on wikipedia (English) page X. You are provided with the list of pages you can go to from page X. Your goal is to go to page Y with the shortest path. (Note that there might be multiple shortest path).

This is a multi-turn game, but I implemented it in single-turn: We provide a part of the shortest path to the LLM [1].

I tried running pre-commit, but I guess it was looking for a python3.11? Which I don't currently have, I'll look at running the pre-commit any way, so you might consider this PR as work-in-progress.

I guess the biggest issue with this PR is the dependency on the datasets python library. The dataset is 62MB.
What's the recommendation there? Should I commit this database as a sqlite somewhere?

I've chosen rewards as:

• 1.0 means that the LLM chose to go to a shortest path
• 0.5 means that the chosen direction isn't the shortest, but only does +1 on the shortest length using that path
• 0.1 means that it managed to do +2 on the shortest length using that path
• 0.01 means that the output is invalid

I have no idea what "levels" parameter of RangeAttributeDefinition are supposed to mean, so it just has the values I copy/pasted from somewhere else.

[1] In this current PR, the length of that prefix path isn't configurable, while it has a big influence on the difficulty

On Gemini 2.5 Pro (Free instance available on openrouter), I get 44% with size=10, seed = 45

[joesharratt1229]

Looks like it will be really useful environment, just a few corrections

[olliestanley]

Rather than using a requirements-optional.txt we can add a section in pyproject.toml containing this dep, as we already do for some other optional requirements