【Feature】add fd plugins && rm model_classes (#3123)

* add fd plugins && rm model_classed

* fix reviews

* add docs

* fix

* fix unitest ci

test/plugins/test_model_registry.py

@@ -0,0 +1,32 @@
+import unittest
+
+from fastdeploy import ModelRegistry
+from fastdeploy.plugins import load_model_register_plugins
+
+
+class TestModelRegistryPlugins(unittest.TestCase):
+    def test_plugin_registers_one_architecture(self):
+        """Test that loading plugins registers exactly one new architecture."""
+        initial_archs = set(ModelRegistry.get_supported_archs())
+        print("Supported architectures before loading plugins:", sorted(initial_archs))
+
+        # Load plugins
+        load_model_register_plugins()
+
+        final_archs = set(ModelRegistry.get_supported_archs())
+        print("Supported architectures after loading plugins:", sorted(final_archs))
+
+        added_archs = final_archs - initial_archs
+        added_count = len(added_archs)
+
+        # verify
+        self.assertEqual(
+            added_count,
+            1,
+            f"Expected exactly 1 new architecture to be registered by plugins, "
+            f"but {added_count} were added: {sorted(added_archs)}",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()