Function humanize_duration 

pub fn humanize_duration(d: Duration) -> String

Convert a Duration to a short human-readable string. Breakpoints chosen to match the cargo / pytest / npm convention:

• < 1ms → "<1ms" (avoid useless 0.0s for very fast no-op runs)
• < 1s → "234ms" (sub-second resolution in ms)
• < 60s → "4.3s" (one decimal place; resolution-vs-noise compromise)
• < 1h → "2m 34s" (no fractional component above a minute)
• ≥ 1h → "1h 5m 12s" (rare for codelore but cheap to support)