refactor: 消除多处重复模式，统一工厂和参数传递

- AutoModel 继承 BaseFactory，消除自建 Registry（-30 行）
- executor.execute_prefill 删除重复 forward 代码块（bug）
- train_callback 移除 Protocol 上矛盾的 issubclass 检查
- engine.py 内部方法统一传 GenerationParams，校验内聚
- protocol.py SSEBuilder 类→函数，handle() 用 GenerationParams
- StreamContext 动态属性改为显式 dataclass 字段
- BaseFactory 新增 get_component_class 方法

astrai/trainer/train_callback.py

@@ -69,12 +69,6 @@ class CallbackFactory(BaseFactory[TrainCallback]):
         callback = CallbackFactory.create("my_callback", **kwargs)
     """
 
-    @classmethod
-    def _validate_component(cls, callback_cls: type) -> None:
-        """Validate that the callback class inherits from TrainCallback."""
-        if not issubclass(callback_cls, TrainCallback):
-            raise TypeError(f"{callback_cls.__name__} must inherit from TrainCallback")
-
 
 @CallbackFactory.register("gradient_clipping")
 class GradientClippingCallback(TrainCallback):