journal client: add a test for real-world message processing
This adds a dump of the messages related to linux.git, and checks that permutations of these messages yield sensible data in the origin visit cache.
This explicitly resets the test fixture before every test to work around the hypothesis limitation wrt function-scoped pytest fixtures.
I'm not sure we really want to land this.
Related to #3000 (closed)
Migrated from D4981 (view on Phabricator)