Instead of retrying HTTP requests only for 429 status code by default,
prefer to use the generic retry policy enabling to also retry for status
codes >= 500 but also on ConnectionError exceptions.
Rename throttling_retry decorator to http_retry to reflect this change.
By using a single equality instead of checking len() then zip()
to check one by one, pytest can find the common/missing elements
and print them nicely when the two lists are unequal.
This removes code and adds support for incremental pagination.
While both are essentially the same lister now, it still makes sense to
keep the Gitea lister separate, in order to:
1. display them in different categories on https://archive.softwareheritage.org/
2. support possible divergence of APIs in the future
