test: update service tests for fixture and API changes

Updates to work with refactored fixtures (no expunge):
- Re-query entities when modifying state in tests
- Remove assertions on expunged object properties

Auth service tests:
- Update to use email_or_username field instead of username

Admin service tests:
- Fix statistics test to use stats_service module
- Remove vendor_name filter test (field removed)
- Update import job assertions

Inventory/Marketplace/Stats/Vendor service tests:
- Refactor to work with attached session objects
- Update assertions for changed response formats
- Improve test isolation and cleanup

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/unit/services/test_product_service.py

@@ -265,18 +265,15 @@ class TestProductService:
     def test_get_inventory_info_success(
         self, db, test_marketplace_product_with_inventory
     ):
-        """Test getting inventory info for product with inventory"""
-        # Extract the product from the dictionary
-        marketplace_product = test_marketplace_product_with_inventory[
-            "marketplace_product"
-        ]
+        """Test getting inventory info for product with inventory."""
+        marketplace_product = test_marketplace_product_with_inventory["marketplace_product"]
+        inventory = test_marketplace_product_with_inventory["inventory"]
 
         inventory_info = self.service.get_inventory_info(db, marketplace_product.gtin)
 
         assert inventory_info is not None
-        assert inventory_info.gtin == marketplace_product.gtin
-        assert inventory_info.total_quantity > 0
-        assert len(inventory_info.locations) > 0
+        assert inventory_info.total_quantity == inventory.quantity
+        assert len(inventory_info.locations) >= 1
 
     def test_get_inventory_info_no_inventory(self, db, test_marketplace_product):
         """Test getting inventory info for product without inventory"""