docs: public Span getCurrentPosition(boolean beforeTid)
      {
          if (getType() == null)
          {
              throw new IllegalStateException("IonReader isn't positioned on a value");
          }
          // Only spans that include the TID octet are seekable.
          IonReaderBinarySpan pos = new IonReaderBinarySpan(beforeTid);
          long start = beforeTid ?  _position_start : _value_start;
          long len = beforeTid ? _position_len : _value_len;
          pos._offset = start - _physical_start_offset;
          pos._limit = pos._offset + len;
          pos._symbol_table = _symbols;
          pos._state = _state;
          return pos;
      }