Add support for XZ compressed metadata #1351
Description
EPEL 9 uses XZ compression on its metadata.
Per the README, this is not a supported compression type, and an issue should be opened when encountering such a situation. EPEL is a very commonly used repository, which I believe it makes a good argument for adding XZ support into RMT.
As it sits, when you attempt to sync this repository RMT silently fails to parse primary.xml, resulting in 0 packages synced, but no error messages.
RMT-REPO-01:~ # rmt-cli mirror repository epel9
I, [2025-07-21T13:38:18.494139 #10575] INFO -- : Mirroring repository epel9 to /usr/share/rmt/public/repo/pub/epel/9/Everything/x86_64/
I, [2025-07-21T13:38:18.744032 #10575] INFO -- : → repomd.xml
I, [2025-07-21T13:38:18.989326 #10575] INFO -- : Repository metadata signatures are missing
I, [2025-07-21T13:38:19.193335 #10575] INFO -- : Total mirrored repositories: 1
I, [2025-07-21T13:38:19.193395 #10575] INFO -- : Total transferred files: 0
I, [2025-07-21T13:38:19.210191 #10575] INFO -- : Total transferred file size: 0 Bytes
I, [2025-07-21T13:38:19.210349 #10575] INFO -- : Total Mirror Time: 00:00:01
I, [2025-07-21T13:38:19.210386 #10575] INFO -- : Mirroring complete.