fix test: prevent MagicMock auto-creating VLM attributes

Use spec=[] on mock model.model to prevent hasattr from
falsely detecting language_model attribute in wrap_fsdp2 tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: RobotSail

tests/test_model_initialization.py

@@ -109,9 +109,9 @@ def mock_model(self):
         model.config = MagicMock()
         model.config.use_cache = True
 
-        # Mock transformer layers
+        # Mock transformer layers (standard CausalLM structure: model.model.layers)
         layers = [MagicMock() for _ in range(4)]
-        model.model = MagicMock()
+        model.model = MagicMock(spec=[])  # spec=[] prevents auto-creating attributes
         model.model.layers = layers
 
         return model