Explain the internal mechanism of `setState` (marking elements dirty).

setState is simply a framework trigger that marks the current Element as 'dirty' and schedules it for a rebuild.

Internally, setState(fn) executes your provided function, then calls element.markNeedsBuild(). This adds the Element to a global _dirtyElements list. During the next frame pipeline (driven by the Engine's Vsync signal), the framework iterates through dirty elements, calling build() to generate new widget configurations, and reconciling the tree.