usage of an index on both cpu and gpu in faiss-rs

index_gpu_use.rs

let res = StandardGpuResources::new()?;

// create an index and place it on GPU memory
let mut index = index_factory(8, "Flat", MetricType::L2)?
    .into_gpu(&res, 0)?;
index.add(get_data())?;

let my_query = get_query();
let result = index.search(&my_query, 5)?;
assert_eq!(result.labels, vec![2, 1, 0, 3, 4]);

// now back to the CPU!
let mut index = index.into_cpu()?;

let result = index.search(&my_query, 5)?;
// should get approximately the same results
assert_eq!(result.labels, vec![2, 1, 0, 3, 4]);