Coregistration GUI modernisation (phase 3)

[payamsash]

Reference issue (if any)

following #14203 and phase 3 of #14141

What does this implement/fix?

add test for coregistration fitting math now so later any algorithmic changes can be (hopefully) caught. I guess from next PRs we could start working on the UI/interactions/algorithms ...

[larsoner]

Because we squash-merged #14203 the commits still show up here and in the diff. Can you rebase the one new commit 45f45b8 and force-push? Personally I would do

git checkout coreg_gui_dev_phase_1_3
git fetch upstream
git reset --hard upstream/main
git cherry-pick 45f45b8
git push origin -f coreg_gui_dev_phase_1_3