Simplify dev tooling, remove colorcet examples, drop 3.7, add 3.12

[maximlt]

Colorcet is a simple package, its dev tooling and infra can be simplified. Principles adopted:

• Keeps things very simple
• Use very standard tools

As a consequence:

• conda is only used when the conda package is built and pushed to pyviz, otherwise it's pip
• no more pyctdev, simple commands are called directly
• no more custom versioning, use setuptools_scm instead
• the site is no longer built directly with nbsite but with sphinx instead
• pyproject.toml only instead of setup.py + setup.cfg
• dropped 3.7 as for some reason pip install -e . wouldn't work on this version (edit: fixed), and added 3.12 since it was easy.

I removed the colorcet examples CLI as it was one less thing to migrate moving from setup.py to pyproject.toml. I guess I could add it again if we want to keep it, although it's a bit annoying as I also moved all the notebook files from /examples to /doc to build with Sphinx directly. Note that Panel removed panel examples is version 1.0.

I thought about moving to hatch/hatchling too in this PR but stuck to setuptools for now, it made my life easier. But from this point on it should be pretty easy to convert to hatch/hatchling if need be.

A change I noticed is that now the sdist has all the tracked files in the repository while it contained less files. This is because setuptools_scm provide a list of all tracked files to setuptools. It could be reduced by pruning dirs and files in MANIFEST.in. I don't see a need to do that.

EDIT:

Happy to report that all the three Github workflows are working with this setup. Also, for some reason I had to update a couple of base images in 012124e. The diff shows that it had something to do with the font more than with the palette.

[hoxbro]

I have noticed in HoloViews that there is some size difference between matplotlib on conda and pip. I think it is around 2px, which could be the difference you are seeing.

[jbednar]

Seems much simpler, thanks. I'm not sure how examples are meant to be obtained now, but I guess it's via the website?

[maximlt]

@jbednar are you ok to merge?