Skip removing apt lists / run updates on each layer?

[jbergstroem]

Chore

Describe the chore

A potential time saving improvement for building containers could be to stop removing the downloaded apt list for the builder / ccache image and avoid updating in each image. I doubt the package repositories have changed between the first image being created and subsequent layer reuse.

Additional context

Happy to open a PR if the approach makes sense. Perhaps there's another reason each step does "update && rm".