lint: correct annotations for Python 3.9.

ldm/invoke/generator/base.py

@@ -2,6 +2,8 @@
 Base class for ldm.invoke.generator.*
 including img2img, txt2img, and inpaint
 '''
+from __future__ import annotations
+
 import os
 import os.path as osp
 import random

ldm/invoke/generator/diffusers_pipeline.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import secrets
 import warnings
 from dataclasses import dataclass

ldm/invoke/model_cache.py

@@ -4,15 +4,20 @@ They are moved between GPU and CPU as necessary. If CPU memory falls
 below a preset minimum, the least recently used model will be
 cleared and loaded from disk when next needed.
 '''
+from __future__ import annotations
+
+import contextlib
 import gc
 import hashlib
 import io
 import os
 import sys
+import textwrap
 import time
 import traceback
 import warnings
 from pathlib import Path
+from typing import Union
 
 import torch
 import transformers