Fix SQLite CI test failures: UUID binding, func.now() defaults, F402 lint

Three fixes from PR #35 review:

1. Fix F402: rename loop var 'table' → 'metadata_table' in test_encrypted_json.py
2. Strip func.now() server_defaults in conftest.py engine/db_engine fixtures
3. Add aiosqlite UUID adapter for async engine

Model changes to provide Python-side defaults for SQLite compatibility:
- TimestampMixin: add default=_utcnow for created_at/updated_at
- UUIDPrimaryKeyMixin: use GuidType for cross-DB UUID handling
- User.id: use GuidType() instead of Text, Mapped[uuid.UUID]
- User.email_verified: add default=False
- Purchase.ingested_at: add default=_utcnow
- types.py: add GuidType TypeDecorator for UUID→String conversion

Fixes: CAR-1012

tests/conftest.py

@@ -8,6 +8,7 @@ import secrets
 import uuid
 from datetime import UTC, datetime, timedelta
 
+import aiosqlite
 import pytest
 from httpx import ASGITransport, AsyncClient
 from sqlalchemy import create_engine, event, text
@@ -19,6 +20,8 @@ from cartsnitch_api.database import get_db
 from cartsnitch_api.main import create_app
 from cartsnitch_api.models import Base
 
+aiosqlite.register_adapter(uuid.UUID, lambda u: str(u))
+
 TEST_JWT_SECRET = secrets.token_urlsafe(32)
 TEST_SERVICE_KEY = secrets.token_urlsafe(32)
 TEST_FERNET_KEY = "7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8="
@@ -58,15 +61,22 @@ def engine():
     """
     eng = create_engine("sqlite:///:memory:")
 
-    for table in Base.metadata.tables.values():
-        for col in table.columns.values():
+    @event.listens_for(eng, "connect")
+    def set_sqlite_pragma(dbapi_connection, connection_record):
+        cursor = dbapi_connection.cursor()
+        cursor.execute("PRAGMA foreign_keys=ON")
+        cursor.close()
+
+    for metadata_table in Base.metadata.tables.values():
+        for col in metadata_table.columns.values():
             sd = col.server_default
             if sd is not None:
                 if not hasattr(sd, "expression"):
                     col.server_default = None
                     continue
                 expr_str = str(sd.expression).lower()
-                if "gen_random_uuid" in expr_str or "gen_random_bytes" in expr_str:
+                _pg_fns = ("gen_random_uuid", "gen_random_bytes", "now()")
+                if any(pg_fn in expr_str for pg_fn in _pg_fns):
                     col.server_default = None
 
     Base.metadata.create_all(eng)
@@ -100,7 +110,8 @@ async def db_engine():
                     col.server_default = None
                     continue
                 expr_str = str(sd.expression).lower()
-                if "gen_random_uuid" in expr_str or "gen_random_bytes" in expr_str:
+                _pg_fns = ("gen_random_uuid", "gen_random_bytes", "now()")
+                if any(pg_fn in expr_str for pg_fn in _pg_fns):
                     col.server_default = None
 
     async with engine.begin() as conn:

tests/test_encrypted_json.py

@@ -18,15 +18,16 @@ from cartsnitch_api.models.user import User, UserStoreAccount
 def engine():
     eng = create_engine("sqlite:///:memory:")
 
-    for table in Base.metadata.tables.values():
-        for col in table.columns.values():
+    for metadata_table in Base.metadata.tables.values():
+        for col in metadata_table.columns.values():
             sd = col.server_default
             if sd is not None:
                 if not hasattr(sd, "expression"):
                     col.server_default = None
                     continue
                 expr_str = str(sd.expression).lower()
-                if "gen_random_uuid" in expr_str or "gen_random_bytes" in expr_str:
+                _pg_fns = ("gen_random_uuid", "gen_random_bytes", "now()")
+                if any(pg_fn in expr_str for pg_fn in _pg_fns):
                     col.server_default = None
 
     Base.metadata.create_all(eng)