GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.
Right now the directory code in tor-dirclient/src/compress.rs supports zlib compression only. It would be good to add support for xz2 and zstd and maybe brotli.
Update (17 Dec 2020): @wuldr has added support for xz2!