docs: public void addItem(int row , int col , double value ) {
          if( nz_length == nz_value.data.length ) {
              int amount = nz_length + 10;
              nz_value.growInternal(amount);
              nz_rowcol.growInternal(amount*2);
          }
          nz_value.data[nz_length] = value;
          nz_rowcol.data[nz_length*2] = row;
          nz_rowcol.data[nz_length*2+1] = col;
          nz_length += 1;
      }