Parial move of reflectometry gui to std::optional

[peterfpeterson]

As part of the modernization work laid out in #37875, this migrates more of the reflectometry interface from boost::optional to std::optional.

The things being intentionally skipped use the following classes as optional:

• string which is involved in the boost::optional<boost::optional<string>> and breaks tests
• double which prompts changes in the sip bindings
• Item
• LookupCriteriaError
• LookupRow
• ProcessingInstructions
• Row
• RowLocation
• Subtree

To test:

This is a refactor so all tests should pass, but poking around with the ISIS reflectometry GUI is a good idea.

This does not require release notes.

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[rbauststfc]

Thanks very much for picking this one up for us! I've not done any functional testing yet, but the code changes are looking good to me and I can't see anything obvious that should be a problem (particularly given that all the tests are passing).

There was just one small thing I had a question about before I start testing the GUI.

[rbauststfc]

Sorry for the delay on the functional testing. I've tested as many of the GUI features as I can, including reducing data manually and using the auto-processing feature, and it's all looking good to me. I can't check live data properly because we're out of cycle, but I've clicked the button to start it up and it displays the message we would expect to see at the moment. I'm sure there won't be any issues with it given the nature of these changes, and we'll still have a chance to test it after this has gone into main.

Thanks again for picking this up for us @peterfpeterson! I will hold off clicking approve until after code freeze to make sure it isn't merged in too early.

@MialLewis, just tagging you in this so that you're aware of it and the wider issue that it's linked to, as there will be more work needed on this in future.

[github-actions]

👋 Hi, @peterfpeterson,

Conflicts have been detected against the base branch. Please rebase your branch against the base branch.