[Frontend] Use new Renderer for Completions and Tokenize API (#32863)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/models/language/pooling/test_mm_classifier_conversion.py

@@ -96,7 +96,7 @@ def test_gemma_multimodal(
         dtype="bfloat16",
     ) as vllm_model:
         llm = vllm_model.get_llm()
-        prompts = llm.preprocess_chat(messages)
+        prompts = llm._preprocess_chat([messages])
 
         result = llm.classify(prompts)
         assert result[0].outputs.probs[0] > 0.95