Disable rate_limit_redis_enabled in test fixtures

The rate-limit middleware creates a Redis client at module import time
when rate_limit_redis_enabled is true. The conftest disables
rate_limit_enabled but not the redis flag, so the client still gets
created. After the test event loop closes, the client's async
disconnect raises 'Event loop is closed', surfacing as 500s on
test_validation_error_returns_422_with_field_errors and
test_error_stats_with_valid_key.

Setting rate_limit_redis_enabled=False in the autouse fixture prevents
the Redis client from being created in the first place.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/conftest.py

@@ -142,8 +142,10 @@ TEST_DATABASE_URL = "sqlite+aiosqlite:///:memory:"
 def disable_rate_limiting():
     """Disable rate limiting for all tests to prevent 429 interference."""
     cartsnitch_settings.rate_limit_enabled = False
+    cartsnitch_settings.rate_limit_redis_enabled = False
     yield
     cartsnitch_settings.rate_limit_enabled = True
+    cartsnitch_settings.rate_limit_redis_enabled = True
 
 
 @pytest.fixture