Add Support for Velocity Arrows in Scatter 3D Graphs

Original issue description:

I propose adding a feature to the scatter and scatter3d graph types in Plotly to support velocity arrows. This feature would allow users to display directional arrows, enhancing data visualization for applications that involve vector fields, velocities, forces, or any data represented by direction and magnitude.

Update 31 Aug 2026:

• 2D quiver now supported with go.Quiver() (as of v7.0.0)
• Our answer for 3D quiver is go.Cone(), but it has limitations:

For 3D though, Cone() isn't really an arrow. To get a velocity vector you have to combine a Cone (head) with a Scatter3d line (shaft) and keep them in sync manually. The bigger issue is that cone size is in data units while line width is in pixels — so on zoom the head and shaft drift out of proportion (head swallows the shaft, or disappears entirely).

What I was after is the 3D analogue of Quiver: takes x, y, z, u, v, w, draws shaft + attached head, with the head sized in pixels so it stays legible under zoom and rotation.

Inizia confrontando gli entry point esistenti go.Quiver() e go.Cone() e il tipo di grafico scatter3d. Definisci come un analogo 3D debba accettare x, y, z, u, v, w e mantenere il proprio fusto e la punta della freccia collegati e leggibili durante lo zoom e la rotazione; il lavoro è completato quando la funzionalità è implementata e il suo comportamento è coperto da test appropriati.