Add ARC-AGI-2 and Kaggle 2025 Datasets (with loader + doc updates)

[jonkaonor]

Hi @mxbi,

Thanks for creating this package, it helps a lot with visualizing ARC tasks! I noticed the dataset folder hasn't been updated with the new ARC-AGI-2 and Kaggle 2025 competition datasets so I've added them and made the associated loader / documentation updates.

Changes:

• Added ARC-AGI-2 dataset (from official repo, merging as done in #6) and Kaggle 2025 competition dataset (from the Kaggle competition data, different merging process). Matched the current JSON format and did basic testing to verify loading / task visualization was working correctly.
• Modified get_data_json to load the new datasets. Changed the latest and kaggle versions to refer to the new datasets since they are the most relevant to current research and competitions.
• Updated README.md with instructions on how to load the new datasets.

Let me know if there are any issues with the changes or modifications you'd suggest!