ITS: test_preview_zoom: improve test runtime speed

Problem: For each frame,
image_processing_utils.convert_image_to_numpy_array and
image_processing_utils.write_image takes around 1 second.

Solution: Replace them with cv2 calls. Total test time reduced from 40+
minutes to less than 15.

Bug: 332322632
Test: test_preview_zoom.py
Change-Id: I26a2e01e8176f2512407f48794f99fed60d785a8