Don't reload graph data on every interaction

[ra3xdh]

I have received a patch providing a fix for #1598 by email. This PR reloads graph data only if it was changes.

[tskaar]

This improves the performance significantly, thanks!

One thing though; currently, if the diagram resizes, one does not do the re-calculation, e.g.

Before stretching

After stretching

The dependency is here:

qucs_s/qucs/diagrams/graph.cpp

Lines 570 to 571 in ad0c643

	auto max_points = std::max(parentDiagram()->boundingRect().width(),
	parentDiagram()->boundingRect().height());

[dsm]

Hi MacOS x86_64 build failed. Fix: QList::assign() compatibility with Qt < 6.6

QList::assign() was introduced in Qt 6.6. Replaced it with the range constructor which has been available since Qt 6.0:

// Before (requires Qt 6.6+)
lines.assign(std::begin(joint_lines), std::end(joint_lines));

// After (works with Qt 6.2+)
lines = QList<QLineF>(std::begin(joint_lines), std::end(joint_lines));

Fixes macOS CI x86_64 build failure.

[ra3xdh]

The build for Qt version less than 6.6 and the problem with resize has been fixed.

[tskaar]

Can confirm the stretching update is now working as expected, thanks!

[ra3xdh]

Merged.