D3 v5 Zoomable Sunburst
This zoomable sunburst chart visualizes hierarchical spending data from the flare.json dataset, with arcs colored by top-level category and sized by expense sums. Users click arcs or the center circle to zoom between hierarchy levels, while labels rotate and fade based on visible arc size. Built with D3 v5, it uses the `d3.partition` layout, `d3.hierarchy`, and arc generators for SVG rendering. Transitions employ `transition.attrTween` and interpolation to animate arc paths and labels smoothly, with style updates handled through attribute tweens and fill-opacity transitions.