[Multimodal][Core] Optimize multimodal preprocessing cache by hashing image bytes instead of pixel values (#29621)

Signed-off-by: Rahul Steiger <rasteiger@ethz.ch>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

tests/entrypoints/pooling/embed/test_online_vision.py

@@ -9,6 +9,7 @@ from transformers import AutoProcessor
 
 from tests.utils import VLLM_PATH, RemoteOpenAIServer
 from vllm.entrypoints.pooling.embed.protocol import EmbeddingResponse
+from vllm.multimodal.base import MediaWithBytes
 from vllm.multimodal.utils import encode_image_base64, fetch_image
 
 MODEL_NAME = "TIGER-Lab/VLM2Vec-Full"
@@ -62,7 +63,11 @@ def get_hf_prompt_tokens(model_name, content, image_url):
 
     placeholder = "<|image_1|> "
     prompt = f"{placeholder}{content}"
-    images = [fetch_image(image_url)]
+    image = fetch_image(image_url)
+    # Unwrap MediaWithBytes if present
+    if isinstance(image, MediaWithBytes):
+        image = image.media
+    images = [image]
     inputs = processor(prompt, images, return_tensors="pt")
     return inputs.input_ids.shape[1]