simplify: dedupe boilerplate and remove dead code across all layers

lib/extensions/date_time.dart

@@ -13,12 +13,8 @@ extension IsSameDay on DateTime {
 
   TimeOfDay toTimeOfDay() => TimeOfDay(hour: hour, minute: minute);
 
-  bool isSameDateTime(DateTime other) {
-    var isSameDay = this.isSameDay(other);
-    var isSameTimeOfDay = (toTimeOfDay() == other.toTimeOfDay());
-
-    return isSameDay && isSameTimeOfDay;
-  }
+  bool isSameDateTime(DateTime other) =>
+      isSameDay(other) && toTimeOfDay() == other.toTimeOfDay();
 
   bool isSameOrAfter(DateTime other) => isSameDateTime(other) || isAfter(other);
 }