feat: cache colors

[s-cerevisiae]

This PR adds cache for colors and palettes, following the practice of tokyonight.nvim. Colorschemes are compiled into a messagepack table on first load, and subsequent loads doesn't load lush.nvim at all. The startup time is reduced to ~2ms on my machine (on par with pre-compiled solution in #235), while allowing for configuration.

Note: a version field is added to zenbones.util which is expected to be updated by release-please. Not sure if it works this way.

Fixes #98.

TODO:

• Fix option cache for randombones
• Add an option to opt-out of caching
• Refactor each colorscheme so that get_global_config is not called twice Not necessary as this only happens once per cache write
• Less duplicated code in term.lua?

[s-cerevisiae]

Okay screw this CI-only tool, I've tried my best but if release-please still doesn't work after merging let's revert all the JSONs and switch to reading a version.txt file that contains 4.12.0 (which should be automatically updated) as I have zero ways to verify the config in action.

[evantravers]

I love this idea… watching with interest.