ingest method
Add pixel delta (already OS-scaled) times multiplier. Returns whole
lines crossed this call (signed). Keeps sub-line remainder in
remainderPx, matching Alacritty's % height retention.
Implementation
int ingest({required double dyPx, required double multiplier}) {
if (cellHeight <= 0) return 0;
_remainderPx += dyPx * multiplier;
final lines = (_remainderPx / cellHeight).truncate();
if (lines != 0) {
_remainderPx -= lines * cellHeight;
}
return lines;
}