fix(ollama): json format mutates caller's messages list in-place (#5539)

mem0/llms/ollama.py

@@ -119,11 +119,12 @@ class OllamaLLM(LLMBase):
         # Handle JSON response format by using Ollama's native format parameter
         if response_format and response_format.get("type") == "json_object":
             params["format"] = "json"
-            # Also add JSON format instruction to the last message as a fallback
+            messages = [dict(m) for m in messages]
             if messages and messages[-1]["role"] == "user":
                 messages[-1]["content"] += "\n\nPlease respond with valid JSON only."
             else:
                 messages.append({"role": "user", "content": "Please respond with valid JSON only."})
+            params["messages"] = messages
 
         # Add options for Ollama (temperature, num_predict, top_p)
         options = {