Add cache to metric prediction_type to speedup (#801)

loading of tasks.

Signed-off-by: Yoav Katz <katz@il.ibm.com>

src/unitxt/task.py

@@ -1,3 +1,4 @@
+from functools import lru_cache
 from typing import Any, Dict, List, Optional, Union
 
 from .artifact import fetch_artifact
@@ -75,11 +76,16 @@ def verify(self):
                 augmentable_input in self.inputs
             ), f"augmentable_input {augmentable_input} is not part of {self.inputs}"
 
+    @staticmethod
+    @lru_cache(maxsize=None)
+    def get_metric_prediction_type(metric_id: str):
+        metric = fetch_artifact(metric_id)[0]
+        return metric.get_prediction_type()
+
     def check_metrics_type(self) -> None:
         prediction_type = parse_type_string(self.prediction_type)
-        for metric_name in self.metrics:
-            metric = fetch_artifact(metric_name)[0]
-            metric_prediction_type = metric.get_prediction_type()
+        for metric_id in self.metrics:
+            metric_prediction_type = FormTask.get_metric_prediction_type(metric_id)
 
             if (
                 prediction_type == metric_prediction_type
@@ -93,7 +99,7 @@ def check_metrics_type(self) -> None:
                 continue
 
             raise ValueError(
-                f"The task's prediction type ({prediction_type}) and '{metric_name}' "
+                f"The task's prediction type ({prediction_type}) and '{metric_id}' "
                 f"metric's prediction type ({metric_prediction_type}) are different."
             )