[LoRA] Add support for pinning lora adapters in the LRU cache (#5603)

vllm/engine/llm_engine.py

@@ -1009,6 +1009,9 @@ class LLMEngine:
     def list_loras(self) -> Set[int]:
         return self.model_executor.list_loras()
 
+    def pin_lora(self, lora_id: int) -> bool:
+        return self.model_executor.pin_lora(lora_id)
+
     def check_health(self) -> None:
         self.model_executor.check_health()