Warn users when picking a non-perceptually-uniform 2D colormap

Warn users when picking a non-perceptually-uniform 2D colormap: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). We ship a bunch of 2D colormaps in the colormaps directory that get used by Volume2D / Vertex2D via the cmap argument. Several of the older ones aren't…