Rough idea: build the bipartite graph of who contributed to which project
Naive implementation: go from each origin (or last visit), and collect every author it references. But there is a lot of duplicate work.
Slightly less naive implementation: reverse-traversal in swh-graph, by tagging every revision/release/snapshot with the set of authors who contributed to their parent, starting from oldest revisions.
This might overflow memory though? If not, could we get away with a database?