[refactor] move rbm.image → image.sub_image

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/tests/test_faces_sub_image.py

@@ -5,7 +5,7 @@ import matplotlib.pyplot as plt
 
 from rbm.model import Model
 from rbm.entity import Entity, EntityParams, TrainingParams
-from rbm.image import SubImage, normalize
+from image.sub_image import SubImage, normalize
 from rbm.matrix import Mat, np, convert
 from rbm.status import CheckpointStatus