Update app.py

revised type and import errors

app.py

@@ -1,15 +1,21 @@
+from __future__ import annotations
+
+from nlp4web_codebase.ir.data_loaders.dm import Document
+from nlp4web_codebase.ir.models import BaseRetriever
+
 from scipy.sparse._csc import csc_matrix
 import numpy as np
 import gradio as gr
 
-from typing import TypedDict
+from typing import TypedDict, Type
 from dataclasses import dataclass
 
 from dataclasses import dataclass
 import pickle
 import os
 from typing import Iterable, Callable, List, Dict, Optional, Type, TypeVar
-from nlp4web_codebase.ir.data_loaders.dm import Document
+from abc import abstractmethod
+
 from collections import Counter
 import tqdm
 import re