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.
Stem uses pycrypto as an optional dependency to validate descriptor signatures. Seems pycrypto is no longer maintained.
Quick search comes up with cryptography and pycryptodome as some possible alternatives.