Doesn't properly detect python depends in .pyi files (cython)

Issue can be reproduced with python-av package as of 14.1.0-1, I didn't check any repo packages for that. There are 180 with .pyi files as of writing this post.

Namcap doesn't detect 2 dependencies:

python-av W: Dependency included, but may not be needed ('python-numpy')
python-av W: Dependency included, but may not be needed ('python-pillow')

These are imported in .pyi files

usr/lib/python3.13/site-packages/av/sidedata/motionvectors.pyi:import numpy as np
usr/lib/python3.13/site-packages/av/audio/frame.pyi:import numpy as np
usr/lib/python3.13/site-packages/av/video/frame.pyi:import numpy as np
usr/lib/python3.13/site-packages/av/video/frame.pyi:from PIL import Image

and trying to run demo from homepage results in an error:

Traceback (most recent call last):
  File "<python-input-8>", line 2, in <module>
    frame.to_image().save(f"frame-{index:04d}.jpg")
    ~~~~~~~~~~~~~~^^
  File "av/video/frame.pyx", line 266, in av.video.frame.VideoFrame.to_image
ModuleNotFoundError: No module named 'PIL'