Fix PIL image cache key collisions across dimensions

[3em0]

PR type

• Bug Fix
• New Feature
• Document Updates
• More Models or Datasets Support

PR information

Fixes #9360.

Template._save_pil_image() used only image.tobytes() to build the image cache hash. Pillow's flattened byte stream does not include mode, width, or height, so images with identical raw bytes but different dimensions could reuse the same cached PNG path.

This PR includes the image mode and dimensions in the hash input before the raw pixel bytes. It also adds a regression test that creates two images from the same bytes with dimensions 120x80 and 80x120, verifies they get different cache paths, and checks that both cached files keep their correct dimensions.

Experiment results

/home/dem0/miniconda3/envs/LLM-HASH/bin/python -m pytest tests/llm/test_template.py::TestTemplate::test_save_pil_image_uses_dimensions_in_cache_key -q
.                                                                        [100%]
1 passed in 3.22s

[gemini-code-assist]

Code Review

This pull request updates the _save_pil_image method to include image metadata (mode, width, and height) in the SHA256 hash calculation, ensuring unique cache keys for images with identical raw bytes but different dimensions. A unit test has been added to verify that different image dimensions result in distinct paths. Review feedback recommends using incremental hash updates to improve memory efficiency when handling large images.

[gemini-code-assist]

For better memory efficiency, especially with large images, you can update the hash object incrementally instead of creating a new concatenated bytes object. This avoids allocating extra memory for the combined metadata and image bytes.

Suggested change

	img_meta = f'{image.mode}:{image.width}:{image.height}:'.encode()
	img_hash = hashlib.sha256(img_meta + image.tobytes()).hexdigest()
	hasher = hashlib.sha256()
	hasher.update(f'{image.mode}:{image.width}:{image.height}:'.encode())
	hasher.update(image.tobytes())
	img_hash = hasher.hexdigest()