Function calculate_distance 

pub fn calculate_distance(lat1: f64, lon1: f64, lat2: f64, lon2: f64) -> f64

Calculate distance between two geographic points using Haversine formula.

Examples

use netspeed_cli::domain::server::calculate_distance;
let dist = calculate_distance(40.7128, -74.0060, 34.0522, -118.2437);
assert!((dist - 3944.0).abs() < 200.0); // ~3944 km, NYC to LA