use std::time::Duration;/// Convert a [`std::time::Duration`] into a human-readable, compact string.////// Formatting rules:/// * < 1 s  ->  "{milli}ms"/// * < 60 s ->  "{sec:.2}s" (two decimal places)/// * >= 60 s ->  "{min}m {sec:02}s"pub fn format_duration(duration: Duration) -> String {    let millis = duration.as_millis() as i64;    format_elapsed_millis(millis)}fn format_elapsed_millis(millis: i64) -> String {    if millis < 1000 {        format!("{millis}ms")    } else if millis < 60_000 {        format!("{:.2}s", millis as f64 / 1000.0)    } else {        let minutes = millis / 60_000;        let seconds = (millis % 60_000) / 1000;        format!("{minutes}m {seconds:02}s")    }}#[cfg(test)]mod tests {    use super::*;    #[test]    fn test_format_duration_subsecond() {        // Durations < 1s should be rendered in milliseconds with no decimals.        let dur = Duration::from_millis(250);        assert_eq!(format_duration(dur), "250ms");        // Exactly zero should still work.        let dur_zero = Duration::from_millis(0);        assert_eq!(format_duration(dur_zero), "0ms");    }    #[test]    fn test_format_duration_seconds() {        // Durations between 1s (inclusive) and 60s (exclusive) should be        // printed with 2-decimal-place seconds.        let dur = Duration::from_millis(1_500); // 1.5s        assert_eq!(format_duration(dur), "1.50s");        // 59.999s rounds to 60.00s        let dur2 = Duration::from_millis(59_999);        assert_eq!(format_duration(dur2), "60.00s");    }    #[test]    fn test_format_duration_minutes() {        // Durations ≥ 1 minute should be printed mmss.        let dur = Duration::from_millis(75_000); // 1m15s        assert_eq!(format_duration(dur), "1m 15s");        let dur_exact = Duration::from_millis(60_000); // 1m0s        assert_eq!(format_duration(dur_exact), "1m 00s");        let dur_long = Duration::from_millis(3_601_000);        assert_eq!(format_duration(dur_long), "60m 01s");    }    #[test]    fn test_format_duration_one_hour_has_space() {        let dur_hour = Duration::from_millis(3_600_000);        assert_eq!(format_duration(dur_hour), "60m 00s");    }}