simvx.editor.panels._properties_instance_section

Instance-side inspector sections + property-row management.

Owns the per-node editable area of the inspector: the Node/Transform/Property sections, multi-selection handling, the property-change handlers that push undo commands, the registry-driven sections, and the collapsible-section bookkeeping. Mixed into :class:PropertiesPanel via _InstanceSectionMixin; the methods live on the panel class through the MRO, so all public/test-visible names stay on PropertiesPanel.