Fix Qt warnings on shutdown

[iche033]

🦟 Bug fix

Fixes #2871

Summary

This fixes the Qt warnings when closing gz sim.

More info:

When a plugin with TreeView is closed, we see warnings about failing to disconnect Qt signals / slots. This is because the tree model used by the TreeView is already destroyed by Qt so the TreeView fails to disconnect their signals / slots. This fix is to manually disconnect all these signals and slots in the tree model destructor so that when deleting the TreeView, it no longer attempts to disconnect them again.

Quick Test:

Launch gz sim -v 4 shapes.sdf, close the window -> you should no longer see Qt warnings like:

(2025-04-22 21:59:49.928) [warning] [Application.cc:922] [GUI] [QT] QObject::disconnect: No such signal QObject::rowsAboutToBeRemoved(QModelIndex,int,int)

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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