popupMenu: release destroyed item signals

[H234598]

Repeated menu rebuilds retain destroyed menu items through managed signal connections. Destroying a submenu can also disconnect parent state handlers that still belong to its siblings.

This change disconnects all parent-managed signals associated with destroyed items, child menus, and sections. A single menu-lifetime handler updates separator visibility and closes submenus, including those inside sections, while preserving the deferred close path used during animations.

Closes #13956.

Regression tests

The regression suite and isolated Xvfb/D-Bus runner are available separately on the tests/popup-menu-signals branch in my fork.

The suite covers 1,000 add/destroy cycles for each of four item types, sibling submenu handling after another submenu is destroyed, separator updates, submenu closure inside sections, and animated/deferred parent closure.

To run the preserved suite:

git clone --branch tests/popup-menu-signals --single-branch https://github.com/H234598/cinnamon.git cinnamon-popup-menu-tests
cd cinnamon-popup-menu-tests
./tests/run-popup-menu-signals.sh

The standalone runner uses the installed Cinnamon runtime and the branch's popup menu implementation. It requires Cinnamon, Xvfb, gdbus, dbus-run-session, setsid, and timeout; it includes compatibility adjustments for running the checkout's popup menu code against the installed Cinnamon 6.6 runtime.

[mtwebster]

Hi can you drop the tests please, just the popupMenu.js changes.

Thanks

[hubyhuby]

Field validation from #14026, the same bug, triggered by the power applet and Bluetooth devices that report their battery level:

I ran the minimal version of this fix (this._signals.disconnect('destroy', menuItem) in _connectItemSignals) on 6.6.9 for 7 days. cinnamon RssAnon stays around 100 MB. Without the fix it reaches ~500 MB within about 4 hours and the session freezes.

@H234598, are you planning to drop the tests as requested?

[H234598]

sure thing, sorry for the delay.

I've removed the two test files as requested, so this PR now contains only the changes to js/ui/popupMenu.js.

The regression tests and isolated Xvfb/D-Bus runner are preserved on the tests/popup-menu-signals branch in my fork.