untilExpiry function
Formats a Duration until expiry as in 5m / in 2h / expired.
Implementation
String untilExpiry(DateTime expiresAt, DateTime now) {
final d = expiresAt.difference(now);
if (d.isNegative) return 'expired';
if (d.inMinutes < 60) return 'in ${d.inMinutes}m';
if (d.inHours < 24) return 'in ${d.inHours}h';
return 'in ${d.inDays}d';
}