Load dynamic module (remote code) only once if code isn't change (#33162)

* Load remote code only once

* Use hash as load indicator

* Add a new option `force_reload` for old behavior (i.e. always reload)

* Add test for dynamic module is cached

* Add more type annotations to improve code readability

* Address comments from code review

tests/models/auto/test_configuration_auto.py

@@ -122,12 +122,27 @@ class AutoConfigTest(unittest.TestCase):
         config = AutoConfig.from_pretrained("hf-internal-testing/test_dynamic_model", trust_remote_code=True)
         self.assertEqual(config.__class__.__name__, "NewModelConfig")
 
+        # Test the dynamic module is loaded only once.
+        reloaded_config = AutoConfig.from_pretrained("hf-internal-testing/test_dynamic_model", trust_remote_code=True)
+        self.assertIs(config.__class__, reloaded_config.__class__)
+
         # Test config can be reloaded.
         with tempfile.TemporaryDirectory() as tmp_dir:
             config.save_pretrained(tmp_dir)
             reloaded_config = AutoConfig.from_pretrained(tmp_dir, trust_remote_code=True)
         self.assertEqual(reloaded_config.__class__.__name__, "NewModelConfig")
 
+        # The configuration file is cached in the snapshot directory. So the module file is not changed after dumping
+        # to a temp dir. Because the revision of the configuration file is not changed.
+        # Test the dynamic module is loaded only once if the configuration file is not changed.
+        self.assertIs(config.__class__, reloaded_config.__class__)
+
+        # Test the dynamic module is reloaded if we force it.
+        reloaded_config = AutoConfig.from_pretrained(
+            "hf-internal-testing/test_dynamic_model", trust_remote_code=True, force_download=True
+        )
+        self.assertIsNot(config.__class__, reloaded_config.__class__)
+
     def test_from_pretrained_dynamic_config_conflict(self):
         class NewModelConfigLocal(BertConfig):
             model_type = "new-model"