TimeWeightedVectorStoreRetriever 在向向量存储插入失败后,会将文档保留在内存中

`TimeWeightedVectorStoreRetriever.add_documents()` adds documents to `memory_stream` before writing them to the vector store. If `vectorstore.add_documents()` raises an exception, the method exits while the documents remain in `memory_stream`. The retriever therefore does not write the documents to the vector store.