fix: fix MLA for ShardedModelLoader/RemoteModelLoader (#6287)

Signed-off-by: wangyu <wangyu.steph@bytedance.com>

python/sglang/srt/model_loader/utils.py

@@ -105,3 +105,15 @@ def get_model_architecture(model_config: ModelConfig) -> Tuple[Type[nn.Module],
 
 def get_architecture_class_name(model_config: ModelConfig) -> str:
     return get_model_architecture(model_config)[1]
+
+
+def post_load_weights(model: nn.Module, model_config: ModelConfig):
+    # Model weight loading consists of two stages:
+    # 1. Initial weight loading.
+    # 2. Post-processing of weights, including assigning specific member variables.
+    # For `dummy_init`, only the second stage is required.
+    if hasattr(model, "post_load_weights"):
+        if model_config.hf_config.architectures[0] == "DeepseekV3ForCausalLMNextN":
+            model.post_load_weights(is_nextn=True)
+        else:
+            model.post_load_weights()