test(image): add --registry-list validation tests and factory comment

- Add test_registry_list_without_registry_fails: validates that
  --registry-list without --registry returns an error
- Add test_registry_list_with_registry_passes: validates the happy path
- Add clarifying comment in factory.py about ECR using OCI adapter

tests/providers/image/lib/registry/test_arguments.py

@@ -73,6 +73,17 @@ class TestValidateArguments:
         ok, _ = validate_arguments(args)
         assert ok
 
+    def test_registry_list_without_registry_fails(self):
+        args = Namespace(images=["nginx:latest"], image_list_file=None, registry=None, image_filter=None, tag_filter=None, max_images=0, registry_insecure=False, registry_list_images=True)
+        ok, msg = validate_arguments(args)
+        assert not ok
+        assert "--registry-list requires --registry" in msg
+
+    def test_registry_list_with_registry_passes(self):
+        args = Namespace(images=[], image_list_file=None, registry="myregistry.io", image_filter=None, tag_filter=None, max_images=0, registry_insecure=False, registry_list_images=True)
+        ok, _ = validate_arguments(args)
+        assert ok
+
     def test_combined_registry_and_image_passes(self):
         args = Namespace(images=["nginx:latest"], image_list_file=None, registry="myregistry.io", image_filter=None, tag_filter=None, max_images=0, registry_insecure=False)
         ok, _ = validate_arguments(args)