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

* add fd plugins && rm model_classed

* fix reviews

* add docs

* fix

* fix unitest ci

fastdeploy/plugins/model_runner/__init__.py

@@ -0,0 +1,32 @@
+"""
+# Copyright (c) 2025  PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+
+from fastdeploy.plugins.utils import load_plugins_by_group, plugins_loaded
+
+# use for modle runner
+PLUGINS_GROUP = "fastdeploy.model_runner_plugins"
+
+
+def load_model_runner_plugins():
+    """load_model_runner_plugins"""
+    global plugins_loaded
+    if plugins_loaded:
+        return
+    plugins_loaded = True
+
+    plugins = load_plugins_by_group(group=PLUGINS_GROUP)
+    assert len(plugins) == 1, "Only one plugin is allowed to be loaded."
+    return next(iter(plugins.values()))