feat: add last_exp_fb to DSTrace and update feedback retrieval usage (#910)

* feat: add last_exp_fb to DSTrace and update feedback retrieval usage

* fix: use trace.last_exp_fb for previous trial feedback description

rdagent/scenarios/data_science/dev/feedback.py

@@ -31,11 +31,9 @@ class DSExperiment2Feedback(Experiment2Feedback):
             exp=sota_exp, heading="SOTA of previous exploration of the scenario"
         )
 
-        last_exp = trace.last_exp()
-
         # Get feedback description using shared template
         feedback_desc = T("scenarios.data_science.share:describe.feedback").r(
-            exp_and_feedback=trace.hist[-1] if trace.hist else None, heading="Previous Trial Feedback"
+            exp_and_feedback=trace.last_exp_fb(), heading="Previous Trial Feedback"
         )
 
         # TODO:

rdagent/scenarios/data_science/proposal/exp_gen/base.py

@@ -304,10 +304,20 @@ class DSTrace(Trace[DataScienceScen, KnowledgeBase]):
         """
         Access the last experiment
         """
-        search_list = self.retrieve_search_list(search_type)
+        if (last_exp_fb := self.last_exp_fb(search_type=search_type)) is not None:
+            return last_exp_fb[0]
+        return None
 
+    def last_exp_fb(
+        self,
+        search_type: Literal["all", "ancestors"] = "ancestors",
+    ) -> tuple[DSExperiment, ExperimentFeedback] | None:
+        """
+        Access the last experiment and feedback
+        """
+        search_list = self.retrieve_search_list(search_type)
         for exp, ef in search_list[::-1]:
-            return exp
+            return exp, ef
         return None
 
     def last_runnable_exp_fb(