keras/src/trainers/data_adapters/data_adapter.py/DataAdapter/batch_size
class DataAdapter:    def batch_size(self):
        """Return the batch size of the dataset created.

        For certain type of the data input, the batch size is known, and even
        required, like numpy array. Whereas for dataset, the batch is unknown
        unless we take a peek.

        Returns:
          int, the batch size of the dataset, or None if it is unknown.
        """
        raise NotImplementedError