[Feature] remove dependency on enable_mm and refine multimodal's code (#3014)

* remove dependency on enable_mm

* fix codestyle check error

* fix codestyle check error

* update docs

* resolve conflicts on model config

* fix unit test error

* fix code style check error

---------

Co-authored-by: shige <1021937542@qq.com>
Co-authored-by: Jiang-Jia-Jun <163579578+Jiang-Jia-Jun@users.noreply.github.com>

fastdeploy/multimodal/registry.py

@@ -0,0 +1,49 @@
+"""
+# 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 typing import Callable
+
+
+class MultimodalRegistry:
+    """
+    A registry for multimodal models
+    """
+
+    mm_models: set[str] = set()
+
+    @classmethod
+    def register_model(cls, name: str = "") -> Callable:
+        """
+        Register model with the given name, class name is used if name is not provided.
+        """
+
+        def _register(model):
+            nonlocal name
+            if len(name) == 0:
+                name = model.__name__
+            if name in cls.mm_models:
+                raise ValueError(f"multimodal model {name} is already registered")
+            cls.mm_models.add(name)
+            return model
+
+        return _register
+
+    @classmethod
+    def contains_model(cls, name: str) -> bool:
+        """
+        Check if the given name exists in registry.
+        """
+        return name in cls.mm_models