Changes

Summary

1. unused (see 123f2c0995b8);
2. tuned;
3. more robust init_built: get_build_id and start_build within the same transaction;
4. tuned: remove redundant guard;
5. maintain short build_id vs. build_uuid, similar to Database_Progress context/context_uuid; clarified database table "isabelle_build_updates";
6. more operations;
7. clarified signature: init_state vs. init_unsynchronized;
8. more thorough "isabelle build_process -C -r -f";
9. more operations;
10. tuned signature;
11. tuned signature: more uniform SQL.Data instances;
12. tuned signature;
13. tuned signature;