stdlib: Make PyStat SimStat inherit from Group

The SimStat Object is nothing more than a group of other SimStats and is
therefore logically a group. With this, functionality can be shared more
easily.

Change-Id: I5dce23a02d5871e640b422654ca063e590b1429a

src/python/m5/ext/pystats/group.py

@@ -54,9 +54,7 @@ class Group(AbstractStat):
             str, Union["Group", Statistic, List["Group"], List["Statistic"]]
         ],
     ):
-        if type is None:
-            self.type = "Group"
-        else:
+        if type:
             self.type = type
 
         self.time_conversion = time_conversion

src/python/m5/ext/pystats/simstat.py

@@ -32,22 +32,16 @@ from typing import (
     Union,
 )
 
-from .abstract_stat import AbstractStat
 from .group import Group
 from .statistic import Statistic
 from .timeconversion import TimeConversion
 
 
-class SimStat(AbstractStat):
+class SimStat(Group):
     """
     Contains all the statistics for a given simulation.
     """
 
-    creation_time: Optional[datetime]
-    time_conversion: Optional[TimeConversion]
-    simulated_begin_time: Optional[Union[int, float]]
-    simulated_end_time: Optional[Union[int, float]]
-
     def __init__(
         self,
         creation_time: Optional[datetime] = None,
@@ -56,10 +50,10 @@ class SimStat(AbstractStat):
         simulated_end_time: Optional[Union[int, float]] = None,
         **kwargs: Dict[str, Union[Group, Statistic, List[Group]]]
     ):
-        self.creation_time = creation_time
-        self.time_conversion = time_conversion
-        self.simulated_begin_time = simulated_begin_time
-        self.simulated_end_time = simulated_end_time
-
-        for key, value in kwargs.items():
-            setattr(self, key, value)
+        super().__init__(
+            creation_time=creation_time,
+            time_conversion=time_conversion,
+            simulated_begin_time=simulated_begin_time,
+            simulated_end_time=simulated_end_time,
+            **kwargs
+        )