Cache BSD packages

[madebr]

When running our ci on BSD platforms (FreeBSD and NetBSD), we download system packages at every run.

Is it possible to cache these downloaded packages in the GitHub cache?
This has 2 main advantages:

• ci might become more reliable (less chance of connection failure)
• our load on the BSD servers will be less (they have to pay less $$$)

[jacob-carlborg]

If the packages rarely change, you can do one better and create a custom VM image [1] with all the things you need preinstalled.

[1] https://github.com/cross-platform-actions/action?tab=readme-ov-file#custom-vm-image-image_url