tests: use tiny 20x20 frames in internvl test_frames_binding to reduce memory
The test only verifies frame count is preserved, not pixel values.
Replacing 448x448 frames with 20x20 (matching tiny processor size) cuts
input tensor size from ~9.6 MB to ~9.6 KB per video, saving ~27 MB.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>