# Description
Get rid of two parallel `Vec`s in `StateDelta` and `EngineState`, that
also duplicated span information. Use a struct with documenting fields.
Also use `Arc<str>` and `Arc<[u8]>` for the allocations as they are
never modified and cloned often (see #12229 for the first improvement).
This also makes the representation more compact as no capacity is
necessary.
# User-Facing Changes
API breakage on `EngineState`/`StateWorkingSet`/`StateDelta` that should
not really affect plugin authors.
