Fix: Add missing OpenAI import in vLLM module (#3091)

mem0/llms/vllm.py

@@ -5,6 +5,7 @@ from typing import Dict, List, Optional
 from mem0.configs.llms.base import BaseLlmConfig
 from mem0.llms.base import LLMBase
 from mem0.memory.utils import extract_json
+from openai import OpenAI
 
 
 class VllmLLM(LLMBase):