COMPAT: alias .to_numpy() for scalars
I think we achieve a bit more consistency in our interfaces if we alias ``.to_numpy()`` to ``.to_datetime64()`` and ``.to_timedelta64()`` for ``Timedelta`` and ``Timestamp`` respectively.

xref https://github.com/pandas-dev/pandas/pull/24486/files#diff-26a6d2ca7adfca586aabbb1c9dd8bf36L235