Consistent ArrayXD Python formatting + better NumPy/Pandas formatting
Return a list of lists instead of a list of NumPy arrays when converting the variable-shaped `ArrayXD` to Python. Additionally, improve the NumPy conversion by returning a numeric NumPy array when the offsets are equal or a NumPy object array when they aren't, and allow converting the variable-shaped `ArrayXD` to Pandas.

(Reported in https://github.com/huggingface/datasets/issues/5719#issuecomment-1507579671)