test: add unit tests for JumpStart network isolation fix

Tests both code paths:
1. _build_for_jumpstart() - verifies enable_network_isolation is applied
   from init_kwargs and that user-set values are not overridden
2. from_jumpstart_config() - verifies enable_network_isolation is
   extracted from deploy_kwargs

Author: lnealrei

sagemaker-serve/tests/unit/test_model_builder_coverage_boost.py

@@ -381,7 +381,7 @@ def test_from_jumpstart_config_basic(self):
         self.assertEqual(mb.model, "test-model")
         self.assertEqual(mb.model_version, "1.0.0")
 
-    @patch("sagemaker.core.jumpstart.artifacts.kwargs._retrieve_model_deploy_kwargs")
+    @patch("sagemaker.serve.model_builder._retrieve_model_deploy_kwargs")
     def test_from_jumpstart_config_applies_network_isolation(self, mock_deploy_kwargs):
         """Test that enable_network_isolation from deploy kwargs is applied."""
         from sagemaker.core.jumpstart.configs import JumpStartConfig
@@ -397,10 +397,14 @@ def test_from_jumpstart_config_applies_network_isolation(self, mock_deploy_kwarg
             model_version="1.0.0"
         )
 
+        mock_session = Mock()
+        mock_session.boto_region_name = "us-west-2"
+
         mb = ModelBuilder.from_jumpstart_config(
             jumpstart_config=js_config,
             role_arn="arn:aws:iam::123456789012:role/SageMakerRole",
             compute=Compute(instance_type="ml.g5.xlarge"),
+            sagemaker_session=mock_session,
         )
 
         self.assertTrue(mb._enable_network_isolation)