Fix SQLite server_default AttributeError and pool_size errors

- Add hasattr(sd, 'expression') guard in engine fixtures to prevent
  AttributeError when iterating over server_default columns that use
  DefaultClause (which lacks .expression)
- Add _build_engine_kwargs() in database.py to conditionally apply
  pool_size/max_overflow only for non-SQLite database URLs
- Fixes test failures in conftest.py, test_encrypted_json.py

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cartsnitch_api/database.py

@@ -6,14 +6,21 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_asyn
 
 from cartsnitch_api.config import settings
 
-engine = create_async_engine(
-    settings.database_url,
-    echo=False,
-    pool_size=10,
-    max_overflow=20,
-    pool_pre_ping=True,
-    pool_recycle=3600,
-)
+
+def _build_engine_kwargs() -> dict:
+    url = settings.database_url
+    kwargs: dict = {"echo": False}
+    if not url.startswith("sqlite"):
+        kwargs.update(
+            pool_size=10,
+            max_overflow=20,
+            pool_pre_ping=True,
+            pool_recycle=3600,
+        )
+    return kwargs
+
+
+engine = create_async_engine(settings.database_url, **_build_engine_kwargs())
 async_session_factory = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)