Simplify code for downloading packages index as gzip and deflate
transfer-encodings are automatically decoded by requests, also
do not stream response for a couple of megabytes and store
HTTP responses in memory.
Also add more debug logs to track lister execution.
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.
