Refactor code structure for improved readability and maintainability

app/db.py

@@ -0,0 +1,23 @@
+from collections.abc import AsyncIterator
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from app.config import settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+engine = create_async_engine(settings.database_url, pool_pre_ping=True)
+session_factory = async_sessionmaker(engine, expire_on_commit=False)
+
+
+async def get_session() -> AsyncIterator[AsyncSession]:
+    async with session_factory() as session:
+        yield session
+
+
+async def close_database() -> None:
+    await engine.dispose()