pyarrow.lib.ArrowNotImplementedError: MakeBuilder: cannot construct builder for type extension<arrow.py_extension_type>
The batch size fix doesn't work... not for #741 and not for this dataset I'm trying (DGS corpus)
Loading the DGS corpus takes 400GB of RAM, which is fine with me as my machine is large enough

I set up a new dataset, with a sequence of arrays (really, I want to have an array of (None, 137, 2), and the first dimension is dynamic) 

```python
    def _info(self):
        return datasets.DatasetInfo(
            description=_DESCRIPTION,
            # This defines the different columns of the dataset and their types
            features=datasets.Features(
                {
                    "pose": datasets.features.Sequence(datasets.features.Array2D(shape=(137, 2), dtype="float32"))
                }
            ),
            homepage=_HOMEPAGE,
            citation=_CITATION,
        )
    def _generate_examples(self):
        """ Yields examples. """

        yield 1, {
            "pose": [np.zeros(shape=(137, 2), dtype=np.float32)]
        }
```

But this doesn't work -
> pyarrow.lib.ArrowNotImplementedError: MakeBuilder: cannot construct builder for type extension<arrow.py_extension_type>
pyarrow.lib.ArrowNotImplementedError: MakeBuilder: cannot construct builder for type extension<arrow.py_extension_type> 
 I set up a new dataset, with a sequence of arrays (really, I want to have an array of (None, 137, 2), and the first dimension is dynamic) 

```python
    def _info(self):
        return datasets.DatasetInfo(
            description=_DESCRIPTION,
            # This defines the different columns of the dataset and their types
            features=datasets.Features(
                {
                    "pose": datasets.features.Sequence(datasets.features.Array2D(shape=(137, 2), dtype="float32"))
                }
            ),
            homepage=_HOMEPAGE,
            citation=_CITATION,
        )
    def _generate_examples(self):
        """ Yields examples. """

        yield 1, {
            "pose": [np.zeros(shape=(137, 2), dtype=np.float32)]
        }
```

But this doesn't work -
> pyarrow.lib.ArrowNotImplementedError: MakeBuilder: cannot construct builder for type extension<arrow.py_extension_type> 
 The batch size fix doesn't work... not for #741 and not for this dataset I'm trying (DGS corpus)
Loading the DGS corpus takes 400GB of RAM, which is fine with me as my machine is large enough
