Note that I'm not modifying anything in the swh-web right now.
I'm just making just conversion happens at the right place so everything is fine. 
 I believe that when we'll be done with typing swh-storage and that we use swh-model objects everywhere.
We can discuss with @anlambert to simplify a bit the "swh-model" used within swh-web (preceding the almost "pervasive" use of our swh.model now), same goes for the archive-data storage used here (preceding the pytest fixtures).
I recall the main swh-model divergence needed here is a way to convert to hex the hashes in bytes and also make the optional value not shown in the main output result.
Like i said, to discuss later ;)
Related to T645