Function extractVictoryLayers

Walks the React element tree to extract Victory data layers into one flat list (single-panel view).

Handles:

• <VictoryChart> wrappers (processes children)
• Standalone data components (e.g. <VictoryScatter>)
• <VictoryStack> for stacked bar charts
• <VictoryGroup> for dodged bar charts, and as a container otherwise