example workflow code for model implementation (#17)

* upload example code for model implementation

* Refactor Model Implement

* add export

---------

Co-authored-by: Young <afe.young@gmail.com>

rdagent/core/implementation.py

@@ -1,13 +1,21 @@
 from abc import ABC, abstractmethod
-from typing import List
+from typing import List, Sequence
 
 from rdagent.core.task import (
+    BaseTask,
     TaskImplementation,
 )
 
 class TaskGenerator(ABC):
     @abstractmethod
-    def generate(self, *args, **kwargs) -> List[TaskImplementation]:
+    def generate(self, task_l: Sequence[BaseTask]) -> Sequence[TaskImplementation]:
+        """
+        Task Generator should take in a sequence of tasks.
+
+        Because the schedule of different tasks is crucial for the final performance
+        due to it affects the learning process.
+
+        """
         raise NotImplementedError("generate method is not implemented.")
 
     def collect_feedback(self, feedback_obj_l: List[object]):