as_PIL option broken in extract_frames_as_images due to _check_cv_dep import behavior

[keighrim]

Bug Description

extract_frames_as_images(..., as_PIL=True) fails with AttributeError: module 'PIL' has no attribute 'Image'.

Cause

_check_cv_dep() (added in 1.3.0) uses importlib.__import__(dep), which returns the top-level package, not the requested submodule. So _check_cv_dep('PIL') returns the PIL namespace package without loading PIL.Image.

[keighrim]

closed via #377