pub async fn nearest<O: Send, M: MeasureDistanceBuilder>(
vector_store: &impl VectorStore,
graph: &impl HnswGraph,
vec: VectorRef<'_>,
on_nearest_fn: impl OnNearestItem<O>,
ef_search: usize,
top_n: usize,
) -> HummockResult<(Vec<O>, HnswStats)>