Packed struct omissions are not FSDB storage classification

Fresh VCS W-2024.09 fixture: packed counter, packed alias, packed inversion, and flat counter. fsdbdebug top_n_var 0 with or without with_computed_signal lists only flat counter. Tree fields share parent IDs. show_ft_var_info reports bus vc_mem counts but no stored/computed label. Keep unknown parents for conservative compression correctness; listing absence does not establish physical storage or reconstruction direction.