LookDevX crashing on connection break

**Describe the bug**
We are seeing an issue with LookDevX that is replicable when building against the latest commits that have been staged for Maya USD 0.29 as well as latest top of tree for 0.30. If we build against the commits for 0.28, we do not see this issue. It seems like an incompatibility that has arisen in between those tags. However we haven't bisected further.

The crash occurs in the graph below if I try to delete the connection between standard_surface1 and Output

**Steps to reproduce**
Steps to reproduce the behavior:
1. Create a Standard Surface shader connected to the Output
2. Disconnect the standard surface shader from the output

We get the following crash. I believe this is a regression since 0.28.

```
Thread 0 Crashed:: CrBrowserMain Dispatch queue: com.apple.main-thread
0 libunwind.dylib 0x18e9d4a68 libunwind::UnwindCursor::step(bool) + 796
1 libobjc.A.dylib 0x1819dd140 objc_addExceptionHandler + 84
2 AppKit 0x18590216c -[NSApplication _commonBeginModalSessionForWindow:relativeToWindow:modalDelegate:didEndSelector:contextInfo:] + 748
3 libqcocoa.dylib 0x1045f3464 QCocoaEventDispatcherPrivate::currentModalSession() + 356
4 libqcocoa.dylib 0x1045f2ab8 QCocoaEventDispatcher::processEvents(QFlags) + 688
5 libExtensionLayer.dylib 0x10c72f8fc 0x10c6f4000 + 243964
6 libExtensionLayer.dylib 0x10c72b534 0x10c6f4000 + 226612
7 libsystem_platform.dylib 0x181dcb584 _sigtramp + 56
8 ??? 0xffff80010c66cec8 ???
9 libLookdevXVnn_1_4.dylib 0x3c1fd0fb0 LookdevX::UfeCommandHook::deleteConnection(VNN_lookdevx_v1::AddRefWrapper const&, VNN_lookdevx_v1::AddRefWrapper const&) + 936
10 libvnnUI_lookdevx_1_0.dylib 0x3eb411f7c TVNNnodeGEModelManager::deleteConnection(VNN_lookdevx_v1::AddRefWrapper const&, VNN_lookdevx_v1::AddRefWrapper const&, bool) + 244
11 libvnnUI_lookdevx_1_0.dylib 0x3eb415778 TVNNnodeGEModelManager::deleteItems(QList const&, QList const&) + 1260
12 libvnnUI_lookdevx_1_0.dylib 0x3eb38ca84 TnodeGEContainerScene::deleteSelectedItems() + 2120
13 QtCore 0x10f3c70c0 void doActivate(QObject*, int, void**) + 1388
14 QtGui 0x10d4ea920 QAction::activate(QAction::ActionEvent) + 368
15 libvnnUI_lookdevx_1_0.dylib 0x3eb45a828 CmpEdImpl::handleShortcut(QKeyEvent*, NodeEditor::TnodeGraphEditorView*) + 768
16 libvnnUI_lookdevx_1_0.dylib 0x3eb3b5320 TnodeGraphEditorNavigationContext::handleKeyPressEvent(QKeyEvent*) + 404
17 QtCore 0x10f37d1b4 QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject*, QEvent*) + 228
18 QtWidgets 0x10df5b244 QApplicationPrivate::notify_helper(QObject*, QEvent*) + 80
19 QtWidgets 0x10df5c368 QApplication::notify(QObject*, QEvent*) + 1044
20 libExtensionLayer.dylib 0x10c73277c 0x10c6f4000 + 255868
21 QtCore 0x10f37d004 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 292
22 QtWidgets 0x10dfb7e40 QWidgetWindow::event(QEvent*) + 204
23 QtWidgets 0x10df5b304 QApplicationPrivate::notify_helper(QObject*, QEvent*) + 272
24 QtWidgets 0x10df5c154 QApplication::notify(QObject*, QEvent*) + 512
25 libExtensionLayer.dylib 0x10c73277c 0x10c6f4000 + 255868
26 QtCore 0x10f37d004 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 292
27 QtGui 0x10d1decf8 QGuiApplicationPrivate::processKeyEvent(QWindowSystemInterfacePrivate::KeyEvent*) + 260
28 QtGui 0x10d2357bc QWindowSystemInterface::sendWindowSystemEvents(QFlags) + 396
29 QtGui 0x10d2353a0 QWindowSystemInterface::flushWindowSystemEvents(QFlags) + 496
30 libqcocoa.dylib 0x10463b158 -[QNSView(Keys) handleKeyEvent:] + 1868
31 libqcocoa.dylib 0x10463c014 -[QNSView(Keys) keyDown:] + 92
32 AppKit 0x1857fbfec -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 480
33 AppKit 0x1857fbc38 -[NSWindow(NSEventRouting) sendEvent:] + 284
34 libqcocoa.dylib 0x1046446b8 -[QNSWindow sendEvent:] + 884
35 AppKit 0x185ec1e70 -[NSApplication(NSEventRouting) sendEvent:] + 1604
36 libqcocoa.dylib 0x1045e716c -[QNSApplication sendEvent:] + 76
37 AppKit 0x185b0f8cc -[NSApplication _handleEvent:] + 60
38 AppKit 0x1856c3cdc -[NSApplication run] + 512
39 libqcocoa.dylib 0x1045f2f28 QCocoaEventDispatcher::processEvents(QFlags) + 1824
40 QtCore 0x10f386c5c QEventLoop::exec(QFlags) + 532
41 QtCore 0x10f37d690 QCoreApplication::exec() + 112
42 libExtensionLayer.dylib 0x10c72cc70 Tapplication::start() + 724
43 Maya 0x10401d35c 0x104008000 + 86876
44 Maya 0x10401cc48 0x104008000 + 85064
45 dyld 0x181a120e0 start + 2360
```

**Specs (if applicable):**
- OS: macOS 14 and macOS 15
- Compiler & version: Apple clang version 15 and 16
- Maya version: Maya 2025.1
- Maya USD commit SHA: fdb1dd6aa879fbd74cc25e53def8a451eb3c578e
- Pixar USD commit SHA: Using the USD Inside Maya