Creating tombstones for tombstones is prohibited in NeoFS system. Metabase
graveyard contains records of the form {address: address}: key is an address
of inhumed object, value is an address of the tombstone. To prevent creation
tombstones for tombstones metabase must control incoming Inhume calls:
* if Inhume target is a tombstone, then "grave" should not be added;
* if {a1:a2} "grave" was created earlier and {a2: a3} "grave" came later,
then first "grave" must be removed as tomb-on-tomb.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
All parameters and resulting values of all metabase operations are
structured in new types. The most popular scenarios for using operations are
moved to auxiliary functions.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
