Base images store out-of-date apt package caches

[lengau]

Bug Description

This is pretty hard to reproduce and not specifically a bug in snapcraft (I put it here to keep it logged somewhere, as I'm unsure where the fix needs to go). @bepri encountered this today when trying to update a snapcraft.yaml file

What happened is that his LXD base image used for snapcraft was created before noble-updates got a cargo-1.85 package, so adding it as a build-package caused craft-parts to fail when trying to install it (because there was no package with that name).

Possible fixes:

0. Asynchronously run apt update on boot.
1. Always update before installing build-packages (up side: gets the latest packages. Down side: very slow)
2. If there are errors when installing build-packages, run update and try again before failing.

This is also the sort of thing that could be worked around by a user if we implemented a purge command for all apps. That's not a fix, but it makes these types of bugs less annoying for users since they don't have to manually mess with the lxd project

To Reproduce

1. Create a snapcraft.yaml file that adds your own PPA or similar.
2. Run snapcraft pack
3. Add a new package (that's not in the Ubuntu repos) to that PPA
4. Add that package to the build-packages for a part

Expected behaviour: It installs that build package

Actual behaviour: It complains that the package does not exist

Environment

n/a

snapcraft.yaml

n/a

Relevant log output

n/a

Additional context

No response