added function to convert duration into a formatted string

lib/services/tools.dart

@@ -4,3 +4,7 @@ String getEnumValueName<T extends Enum>(T value) {
   name = name[0].toUpperCase() + name.substring(1);
   return name;
 }
+
+String durationToFormattedString(Duration duration) {
+  return '${duration.inHours}h ${duration.inMinutes % 60}m';
+}