D3-7: Enter, Exit, Update
This example demonstrates D3’s enter, exit, and update pattern with a fruit-themed dataset. Five apples render as red circles in a rounded steelblue bowl; after two seconds, one apple is removed, and after four more, the third apple becomes a lemon, changing its size and color. The `rend` function uses `selectAll`, `data`, and `.enter().append()` to create circles and text, `.merge()` to update attributes via `transition().duration(1000)`, and `.exit().remove()` to delete elements. It relies on `scaleOrdinal` for color and radius mappings, with two `setTimeout` calls triggering updates.