public String toString(boolean concise, long n) {
            if (concise) {
                return this.conciseString;
            }
            return n == 1 ? this.formalStringSingular : this.formalStringPlural;
        }
Formats {@code duration} as a string, either in a {@code concise} (1 letter)
or full length format, displaying all possible elements.

@param duration the duration
@param concise  if the output should be concisely formatted
@return the formatted string
helper/src/main/java/me/lucko/helper/time/DurationFormatter.java