Increase default colormap size to 256 colors, add colormap BISTs (bug #65010) * autumn.m, bone.m, cool.m, copper.m, cubehelix.m, flag.m, gray.m, hot.m, hsv.m, jet.m, lines.m, ocean.m, prism.m, rainbow.m, spring.m, summer.m, turbo.m, viridis.m, white.m, winter.m: Change default return size from 64 to 256. Update docstring text about colormap size being either the size of the current colomap or the default of 256. Add function BISTs for calling forms and input validation. * colorcube.m: Update input validation to match other colormaps. Change default return size from 64 to 256. Update docstring text about colormap size being either the size of the current colomap or the default of 256. Add function BISTs for calling forms and input validation. * colormap.m: Update default colormap size to 256. Add docstring noting new colormap size and that colormap will create a new figure if one does not exist. Update BISTs for new size. * graphics.cc (viridis_colormap): Replace 64 color interpolated viridis map table with full 256 color map. Increase cmap container size to 256. * NEWS.10.md: Note increased size of default return from colormap functions.

--- a/etc/NEWS.10.md	Sat Dec 23 14:14:26 2023 +0100
+++ b/etc/NEWS.10.md	Mon Dec 25 18:35:50 2023 -0500
@@ -16,6 +16,9 @@
 
 - `height` and `width` are now aliases for the `rows` and `columns` functions.
 
+- All colormaps now default to a size of 256 colors. (The previous default
+size was 64.
+
 ### Alphabetical list of new functions added in Octave 10
 
 * `rticklabels`