Implement efficient node rendering and a basic interaction API

[KrLiam]

This pull request introduces the following changes:

• Split node spawning from scope resolution into two independent systems.
• Optimize node property modifications, allowing partial property updates without node respawn.
• Add robust scope-based variable/property resolution for styles, widgets and layouts.
• Resolve variables using dependency graphs and topological sorting to guarantee evaluation correctness.
• Allow classes to be changed during runtime to unlock dynamic style activation/deactivations.
• Automatically insert Bevy's Interaction component on elements with the interactable class.
• Add the hovered and pressed classes to elements based on their interaction state.
• Add class-related API to NekoUINodes for adding, removing, toggling and testing for classes in elements during runtime.