[Feature Request] some features for public CI setups

[Roger-luo]

There are some CI works that need to be done for this package and some will be quite useful
in general for the community, I list them in priorities (higher has higher priority)

• custom GitHub runners to make our tests run faster
• a way to show temporary doc builds as static webpages
• faster documentation generation by caching system image
• downloadable system image for common platforms

cc: @lightbiaggi