fix get rag llm error

metagpt/rag/factories/llm.py

@@ -10,7 +10,7 @@ from llama_index.core.llms import (
     LLMMetadata,
 )
 from llama_index.core.llms.callbacks import llm_completion_callback
-from pydantic import Field, model_validator
+from pydantic import Field
 
 from metagpt.config2 import Config
 from metagpt.llm import LLM
@@ -30,19 +30,30 @@ class RAGLLM(CustomLLM):
     num_output: int = -1
     model_name: str = ""
 
-    @model_validator(mode="after")
-    def update_from_config(self):
+    def __init__(
+        self,
+        model_infer: BaseLLM,
+        context_window: int = -1,
+        num_output: int = -1,
+        model_name: str = "",
+        *args,
+        **kwargs
+    ):
+        super().__init__(*args, **kwargs)
         config = Config.default()
-        if self.context_window < 0:
-            self.context_window = TOKEN_MAX.get(config.llm.model, DEFAULT_CONTEXT_WINDOW)
+        if context_window < 0:
+            context_window = TOKEN_MAX.get(config.llm.model, DEFAULT_CONTEXT_WINDOW)
 
-        if self.num_output < 0:
-            self.num_output = config.llm.max_token
+        if num_output < 0:
+            num_output = config.llm.max_token
 
-        if not self.model_name:
-            self.model_name = config.llm.model
+        if not model_name:
+            model_name = config.llm.model
 
-        return self
+        self.model_infer = model_infer
+        self.context_window = context_window
+        self.num_output = num_output
+        self.model_name = model_name
 
     @property
     def metadata(self) -> LLMMetadata: