Lower parquet row group size for image datasets
REQUIRES test_get_writer_batch_size to be merged, and to update the `datasets` version to use this feature.

This should help optimize random access to parquet files for https://github.com/huggingface/datasets-server/pull/687/files
Lower parquet row group size for image datasets: REQUIRES test_get_writer_batch_size to be merged, and to update the `datasets` version to use this feature.

This should help optimize random access to parquet files for https://github.com/huggingface/datasets-server/pull/687/files