sS formatDays(Duration d, int decimals default 1) {
  ret formatDays(toMS(d), decimals);
}

sS formatDays(long ms, int decimals default 1) {
  ret formatDays(toDays(ms), decimals);
}
  
sS formatDays(double days, int decimals default 1) {
  S formatted = formatDouble(days, decimals);
  ret eq(formatted, "1") ? "1 day" : formatted + " days";
}

Began life as a copy of #1036176