DirectoryLoader: Check nar hashes when provided
The lister now provides the "checksums_computation". This is either "standard" (for most cases as in bare checksums on the object retrieved) or "nar" for some edge case. In that case the computation is delegated to the "nix-store" command (which should be present in the system running the loading).
This adapts the directory loader to deal with this case.
No work has been done for the ContentLoader yet besides failing the case if a call happens with such case.
Related to T3781 Depends on swh/infra/ci-cd/swh-jenkins-dockerfiles!49 (closed)
Migrated from D8618 (view on Phabricator)