code: def search_knn(self, query_vectors: np.array, top_docs: int):
      raise NotImplementedError
  
imports: import os
  import logging
  import pickle
  import faiss
  import numpy
label_desc: Use image node_id 3 for calling the DenseIndexer obj's underlying member method code with example usage: obj.search_knn(query_vectors, top_docs) without return types