Code Review

This pull request introduces asynchronous wrappers (aprepare_retriever and acall) for blocking RAG operations, utilizing asyncio.to_thread to prevent stalling the event loop. It also updates simple_chat.py and websocket_wiki.py to leverage these async methods and offload blocking calls like RAG initialization and file retrieval to worker threads. The review feedback highlights a critical issue with instantiating asyncio.Semaphore at the module level, which can lead to runtime errors due to binding to an inactive or incorrect event loop, and suggests lazily initializing the semaphore within the async method instead.