WP-1461 spike: uPlot demos

Synthetic patterns drawn by the prototypes the WP measured. Each page times what you do and prints it in the toolbar.

• The pattern plot, 59 498 points: three linked panes, every gesture, the exports
• The same, every marker drawn (decision D5)
• The same at 200 000 points, the ceiling D4 needs
• Series trajectory, compare overlay and an in-situ map

What write_html writes, from the same 22 003-point arrays:

• on uPlot (1.63 MB)
• on plotly, as it is today (6.53 MB)