append method
Appends one encoded document and returns its offset inside the payload.
Implementation
int append(Bytes doc) {
if (_finished) throw StateError('block already finished');
final size = doc.length;
_ensure(_pos + size);
_buffer.setRange(_pos, _pos + size, doc.asUint8List());
final relative = _pos - blockHeaderSize;
_pos += size;
_count++;
return relative;
}