Use-after-free in KV backends via leaked `affinitypool::spawn_local` future

The kv-mem, kv-surrealkv and kv-rocksdb backends move non-'static borrowed state into affinity-pool closures through affinitypool::spawnlocal: a tokio::sync::MutexGuard, &Transaction, &mut ScanStateKeys/Vals, &mut dyn KeyVisitor/ValVisitor, RwLockReadGuard, and a ReadOptions holding a raw...