copyFrom method
Copies len cells from src starting at srcCol to dstCol at this
line.
Implementation
void copyFrom(BufferLine src, int srcCol, int dstCol, int len) {
resize(dstCol + len);
_data.setRange(
dstCol * _cellSize,
(dstCol + len) * _cellSize,
src.data,
srcCol * _cellSize,
);
version++;
}