fix: Ensure proper closure of database session with asyncio shield

[YoshihitoAso]

📌 Description

Fixed asynchronous database session closes to be protected from cancellation.

✅ Related Issues

• Related to feat: Change Gunicorn worker class to standard ASGI #1750

🔄 Changes

Async database session management:

• The db_async_session function now uses asyncio.shield to protect the db.close() call from cancellation, ensuring the session is properly closed even if the coroutine is cancelled.

📌 Checklist

• I have added tests where necessary.
• I have updated the documentation where necessary.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
app/database
__init__.py	50	12	76%	48, 55, 73, 109–111, 113, 123–124, 132–133, 135
TOTAL	46102	1557	96%

Tests	Skipped	Failures	Errors	Time
1504	0 💤	0 ❌	0 🔥	12m 16s ⏱️