formatCompact method
Formats as a compact string.
Implementation
String formatCompact() {
final parts = <String>[];
if (years > 0) parts.add('${years}y');
if (months > 0) parts.add('${months}mo');
if (days > 0) parts.add('${days}d');
if (hours > 0) parts.add('${hours}h');
if (minutes > 0) parts.add('${minutes}m');
if (seconds > 0 || parts.isEmpty) parts.add('${seconds}s');
return parts.join(' ');
}