Update banned users handling with async support and improved date parsing

- Modified `change_page` function in `callback_handlers.py` to use async methods for retrieving banned users and their buttons.
- Enhanced `get_banned_users_list` in `helper_func.py` to handle string timestamps and various date formats, ensuring robust date parsing.
- Added a new test case in `test_utils.py` to validate the handling of string timestamps in the banned users list retrieval.

helper_bot/handlers/callback/callback_handlers.py

@@ -219,14 +219,14 @@ async def change_page(
             reply_markup=keyboard
         )
     else:
-        message_user = get_banned_users_list(int(page_number) * 7 - 7, bot_db)
+        message_user = await get_banned_users_list(int(page_number) * 7 - 7, bot_db)
         await call.bot.edit_message_text(
             chat_id=call.message.chat.id, 
             message_id=call.message.message_id,
             text=message_user
         )
         
-        buttons = get_banned_users_buttons(bot_db)
+        buttons = await get_banned_users_buttons(bot_db)
         keyboard = create_keyboard_with_pagination(page_number, len(buttons), buttons, 'unlock')
         await call.bot.edit_message_reply_markup(
             chat_id=call.message.chat.id,