Removed

• deepclone_hydrate() no longer treats the special "\0" key as SPL
  internal state. ArrayObject, ArrayIterator, and SplObjectStorage
  all ship __serialize / __unserialize since PHP 7.4 — callers can
  populate them by instantiating with deepclone_hydrate() and calling
  __unserialize() with the documented array shape, or by round-tripping
  via deepclone_from_array() which routes through __unserialize
  natively. The mangled-key resolution path ("propName", "\0*\0prop",
  "\0Class\0prop") is unchanged.

  This removes ~80 lines of bespoke SPL handling — offsetSet loops,
  constructor invocation, packed-array shape validation, error paths —
  that duplicated what the classes natively expose. Symfony's
  Hydrator::hydrate() / Instantiator::instantiate() retain BC by
  translating the legacy "\0" shape to __unserialize() in user-land.