[WIP] Similarity, SNL, and provenance bulders

[esoteric-ephemera]

• Add builders for similarity, updating experimental SNL collections, and updating provenance builder as needed
• Normalize document models for DB SNLs:
  • Removed some fields which...:
    • ...contain no data (task_dict, state_details)
    • ...only contain the same information (state which is only ever COMPLETED or None; parameters which is only ever {'priority': 1000, 'boltztrap': False} if not None)
    • ...which duplicate information in StructureMetadata (reduced_cell_formula_abc, chemsystem)
    • ...which have no clear interpretation (_bt, "build time"?)