Refactor endpoint /program/year/month/day

Refactored remaining endpoint /program/<int:year>/<int:month>/<int:day>/ to use mixin class instead of plain function and added annotations.

Date handling tested using debug print statements - so needs further testing.

program/views.py

@@ -147,7 +147,7 @@ class APIDayScheduleViewSet(
     mixins.ListModelMixin,
     viewsets.GenericViewSet,
 ):
-    queryset = Schedule.objects.all()
+    queryset = TimeSlot.objects.all()
 
     def list(self, request, year=None, month=None, day=None):
         # datetime.combine returns a timezone naive datetime object