py : fix flake8 and isort nitpicks (#960)

convert.py

@@ -18,10 +18,12 @@ import zipfile
 from abc import ABCMeta, abstractmethod
 from dataclasses import dataclass
 from pathlib import Path
+from typing import (IO, TYPE_CHECKING, Any, Callable, Dict, Iterable, List,
+                    Literal, Optional, Sequence, Tuple, TypeVar, Union)
+
 import numpy as np
 from sentencepiece import SentencePieceProcessor  # type: ignore
-from typing import (IO, Any, Callable, Iterable, Literal, Optional, Sequence,
-                    TypeVar, Union, List, Dict, Tuple, TYPE_CHECKING)
+
 if TYPE_CHECKING:
     from typing_extensions import TypeAlias