P0 of the SetDisks split (tracking backlog#815). Introduce SetDisksCtx<'a>,
a Copy borrow handle over the shared SetDisks core state (topology/config,
disks, locker trio), and validate the pattern by routing the List family's
delete_all through a ListOperations<'a> service unit.
No trait impl is moved and runtime behavior is byte-for-byte unchanged; the
public SetDisks::delete_all entry point is preserved and delegates to the
borrow-based unit.
Zhengchao An