fix(datatypes): fix bad references in to_numpy()

[deepyaman]

Description of changes

Fix bad reference to NumpyFormat; use NumpyType as in the other to_* methods.

Issues closed

Calling .to_numpy() on a DataType object resulted in:

*** ImportError: cannot import name 'NumpyFormat' from 'ibis.formats.numpy' (/opt/miniconda3/envs/pandera-dev/lib/python3.11/site-packages/ibis/formats/numpy.py)

[jcrist]

Thanks! Can you add a test (I think in ibis/expr/datatypes/tests/test_core.py) that would hit this code path?

[deepyaman]

Thanks! Can you add a test (I think in ibis/expr/datatypes/tests/test_core.py) that would hit this code path?

Added a test. Not sure if there's a better way to get roundtripable types, but this should be sufficient (given that formats are already tested)?

[jcrist]

Thanks!