ENH: (CLI): support colormap extension packages other than cblind (cmasher, cmocean, cmyt)

[neutrinoceros]

In the process of removing cblind as a requirement, I also added support for other known colormap packages if they are installed. I'll need to add test coverage too before I undraft.

[neutrinoceros]

Note that I'm intentionally not including cmasher in test_all.txt because including creates a new failure mode when installing via uv: colorspacious (which cmasher depends on) raises a SyntaxWarning the first time it is imported. This can be worked around by passing --compile-bytecode to uv pip install but I just don't want to add this layer of complexity to this CI.