Fix: Address blocking file operation in log (jcwillox#145)

- Resolved Home Assistant warning about blocking file operations in the `auto_backup` integration (jcwillox#145).
- Updated `handlers.py` to replace synchronous `open` calls with `aiofiles.open` for non-blocking file writes.
- Improved compatibility with Home Assistant's asyncio architecture, preventing event loop warnings.
- Verified changes to ensure integration functionality remains intact.

custom_components/auto_backup/handlers.py

@@ -1,3 +1,4 @@
+import aiofiles
 import asyncio
 import logging
 import shutil
@@ -141,13 +142,13 @@ async def download_backup(
                 if request.status not in (200, 400):
                     _LOGGER.error("%s return code %d.", command, request.status)
                     raise HassioAPIError()
-
-                with open(destination, "wb") as file:
+                
+                async with aiofiles.open(destination, "wb") as file:
                     while True:
                         chunk = await request.content.read(CHUNK_SIZE)
                         if not chunk:
                             break
-                        file.write(chunk)
+                        await file.write(chunk)
 
                 _LOGGER.info("Downloaded backup '%s' to '%s'", slug, destination)
                 return