Re design the lazy loading feature for Content objects
While working on swh-model#2422 (closed), it appeared that the way lazy loading of disk file backed Content objects suffers from design problems, and moreover, is actually not used any more in (loader implementations nor any other package).
Making the lazy-loading mechanism properly work and used could bring a significant gain in memory usage of some parts of the stack (loaders most probably, maybe others).
Migrated from T2466 (view on Phabricator)