fix: Use pyarrow_hotfix everywhere

[paleolimbot]

Ensures that pyarrow_hotfix is imported everywhere we import pyarrow.

[jorisvandenbossche]

(FWIW, I think it should be sufficient to import it once in the __init__.py)

[kylebarron]

Agreed, the top-level __init__.py always gets imported first, so you should only need it there