fix(tests): invalidate default registry cache in cp alias tests

The test_cli_cp_alias and test_python_cp_alias tests were failing
because they sync new registry data but the global _default_registry_cache
was not being invalidated. This caused the tests to use a stale cached
registry that didn't include the newly synced models.

The fix resets _default_registry_cache to None after syncing, forcing
get_default_registry() to reload all registries from the cache when
the copy functions are called.

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: wpbonelli

autotest/test_models.py

@@ -586,6 +586,10 @@ def test_cli_cp_alias(self, tmp_path):
         result = source.sync(ref=TEST_MODELS_REF)
         assert len(result.synced) == 1
 
+        # Invalidate cached default registry so it reloads with newly synced data
+        import modflow_devtools.models
+        modflow_devtools.models._default_registry_cache = None
+
         # Load registry and get first model name
         registry = _DEFAULT_CACHE.load(TEST_MODELS_SOURCE_NAME, TEST_MODELS_REF)
         assert len(registry.models) > 0
@@ -619,6 +623,10 @@ def test_python_cp_alias(self, tmp_path):
         result = source.sync(ref=TEST_MODELS_REF)
         assert len(result.synced) == 1
 
+        # Invalidate cached default registry so it reloads with newly synced data
+        import modflow_devtools.models
+        modflow_devtools.models._default_registry_cache = None
+
         # Load registry and get first model name
         registry = _DEFAULT_CACHE.load(TEST_MODELS_SOURCE_NAME, TEST_MODELS_REF)
         assert len(registry.models) > 0