Samples lose their metadata when going through PipelineSimple

Somewhere in the pipeline, the metadata of the references and probes (age, gender, ...) are lost. They are no longer available in the score files.

Issue encountered with bob bio pipeline simple mobio-all arcface-insightface.

After a first investigation:

• The metadata attributes are present when creating the Sample objects with the Database.
• The ScoreWriter receives Sample objects that are already missing those attributes.
• The Distance BioAlgorithm seems to transform samples into bags. Maybe more investigation needed here.