rpm-ostree should be very respectful of user bandwidth

[da2ce7]

on Fedora Linux 38.20230915.0 (Silverblue)

part of:

• #2560

Problem:

rpm-ostree wastes (significant) user bandwidth when exiting uncleanly

The entire update and download process is restated if exited uncleanly.

User Experience:

Users in less developed countries that hasve slow internet connections may take days to download an update, however they often shut down their computer at night and thus uncleadly end the update proceeds.

Leading to the loss of precious bandwidth.

Expected Behavior:

Downloading objects should be resilient to the loss of power and all other interruptions. Downloads should resumed and correctly downloaded pieces should be cached and made available for the next attempt.

Would you like to work on the issue?

For the moment I'm working on unrelated bittorrent infrastructure; I believe that downloading data in reliable and secure way is already a solved problem.