Implicit type conversion of lists in to_pandas
### Describe the bug

```
ds = Dataset.from_list([{'a':[1,2,3]}])
ds.to_pandas().a.values[0]
```
Results in `array([1, 2, 3])`  -- a rather unexpected conversion of types which made downstream tools expecting lists not happy.

### Steps to reproduce the bug

See snippet

### Expected behavior

Keep the original type

### Environment info

datasets 2.6.1
python 3.8.10