Convert other schema types (polars, numpy, pandas, python) to narwhals type

[ptomecek]

Is your feature request related to a problem? Please describe.
It would be convenient if dtypes could be more flexibly specified:
https://github.com/Point72/ccflow/blob/main/ccflow/exttypes/narwhals.py#L143

Describe the solution you'd like
Extend the validator to handle more types.