feat: 🎸 change the meaning of a "valid" dataset
Now: a dataset is considered valid if "at least one split" is valid.

BREAKING CHANGE: 🧨 /valid and /is-valid consider as valid the datasets with at least one
valid split (before: all the splits were required to be valid)

Fixes https://github.com/huggingface/datasets-preview-backend/issues/139
feat: 🎸 change the meaning of a "valid" dataset: Now: a dataset is considered valid if "at least one split" is valid.

BREAKING CHANGE: 🧨 /valid and /is-valid consider as valid the datasets with at least one
valid split (before: all the splits were required to be valid)

Fixes https://github.com/huggingface/datasets-preview-backend/issues/139