Function measure_latency_under_load 

pub async fn measure_latency_under_load(
    client: Client,
    url: String,
    samples: Arc<Mutex<Vec<f64>>>,
    stop_signal: Arc<AtomicBool>,
)

Measure latency while running a bandwidth test.

This runs in the background during download/upload tests to measure latency under load (bufferbloat detection).