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