The original test json string contained largely default/empty values so it is hard to tell whether they are really being loaded. Add a new string containing fully populated values as well as an "empty" batch representation containing defaults. Use these for the main window containing two batches.

Add a new unit test to test the case where the instrument has changed.

Re #28429

Also updated class_maker.py

This commit replaces all header guards in qt/scientific_interfaces with #pragma once.

Re #27889

These are now injected into the main window presenter's constructor so
that they can be tested.

Re #27242