fix: split-descriptive-statistics fails for datasets with list features
While reviewing https://github.com/huggingface/datasets-server/issues/1443 I found that for the first error AttributeError, there is a minor bug in split-descriptive-statistics, it fails when features include list (sequences).
After this fix, we should force-refresh cached records for:
```
db.cachedResponsesBlue.countDocuments({error_code:"UnexpectedError", "details.copied_from_artifact":{$exists:false}, "details.cause_exception":"AttributeError",kind:"split-descriptive-statistics"})
9748

```
fix: split-descriptive-statistics fails for datasets with list features: While reviewing https://github.com/huggingface/datasets-server/issues/1443 I found that for the first error AttributeError, there is a minor bug in split-descriptive-statistics, it fails when features include list (sequences).
After this fix, we should force-refresh cached records for:
```
db.cachedResponsesBlue.countDocuments({error_code:"UnexpectedError", "details.copied_from_artifact":{$exists:false}, "details.cause_exception":"AttributeError",kind:"split-descriptive-statistics"})
9748

```