Use effective profile instead of an entirely new default profile when loading profiles

[tgreenx]

Purpose

This PR proposes to use effective profile instead of an entirely new default profile when loading profiles in Backend. This means that missing values are filled from the effective profile instead of the default profile, in case any were changed. Note that the effective profile is initially instantiated from the default profile.

Context

See #1192 (review).

Fixes #1191
Replaces #1192

How to test this PR

Unit tests are updated and should pass.

[matsduf]

We are late in the testing cycle for the v2024.2 release. This PR affects how things are tested whereas #1192 only affects how the unit tests are run. Wouldn't it be safer to merge #1192 now and then, after the release merge this unless we find any issues with it? This would mean that we do not have to review and test this before the release.

If/when this is merged, t/test01.t could be cleaned up and the changes from #1192 could be reverted. The t file could win on some restructuring anyway.

[tgreenx]

We are late in the testing cycle for the v2024.2 release. This PR affects how things are tested whereas #1192 only affects how the unit tests are run. Wouldn't it be safer to merge #1192 now and then, after the release merge this unless we find any issues with it? This would mean that we do not have to review and test this before the release.

If/when this is merged, t/test01.t could be cleaned up and the changes from #1192 could be reverted. The t file could win on some restructuring anyway.

Yes I agree, fine with me.

Fine for v2025.1 release. Needs reviewing and testing first.

[mattias-p]

While I haven't yet looked into the problem or how this change would solve it, the change is giving me bad vibes. I need to take a closer look, but I'll get back to it later since it's been pushed to the next release.