Allow use of Html.lazy / Svg.lazy?

[Janiczek]

I wish elm-charts allowed for using Html.lazy / Svg.lazy for particular parts of the chart, so that you could only pay the rendering work once for the actual chart and then compute only the interactive stuff as your hovering : List ... changed.

Right now it seems we're paying the whole view cost at all times. Wrapping C.chart in Html.Lazy helps shield it from unrelated Msgs, but still, for the actual interactivity of the chart, it feels like it should be possible to factor rendering the actual SVG chart away from the rendering of the interactive stuff (lines, tooltips, ...).