code: public YearWeek plusYears(long yearsToAdd) {
          if (yearsToAdd == 0) {
              return this;
          }
          int newYear = Math.toIntExact(Math.addExact(year, yearsToAdd));
          return withYear(newYear);
      }
docs: Returns a copy of this year-week with the specified number of years added.
  <p>
  If the week of this instance is 53 and the new year does not have 53 weeks,
  the week will be adjusted to be 52.
  <p>
  This instance is immutable and unaffected by this method call.
  
  @param yearsToAdd  the years to add, may be negative
  @return the year-week with the years added, not null