fix: Remove unused imports from sendchat.py and add hashlib import in models.py

aider/models.py

@@ -6,6 +6,7 @@ import os
 import platform
 import sys
 import time
+import hashlib
 from dataclasses import dataclass, fields
 from pathlib import Path
 from typing import Optional

aider/sendchat.py

@@ -1,11 +1,5 @@
-import hashlib
-import json
-import os
-import time
 
 from aider.dump import dump  # noqa: F401
-from aider.exceptions import LiteLLMExceptions
-from aider.llm import litellm
 from aider.utils import format_messages
 
 # from diskcache import Cache