Previous change in there (d0cf4a4a8b, in 4.3 only) reverted
retiming keys to have one draw call per strip again. Which gets fairly
expensive if many strips have retiming keys.
However! All the strips are already drawn in two parts: all the regular
strips first, and then all the strips that are being "dragged over"
the other strips. So we can totally draw retiming keys for the whole
batch of strips at once, and it will just work out fine.
Viewing whole Sprite Fright Edit v135 timeline, on PC (Ryzen 5950X,
Win10/VS2022): draw_timeline_seq 7.4ms -> 5.8ms
(sequencer_retiming_keys_draw part 1.7ms -> 0.3ms)
Pull Request: https://projects.blender.org/blender/blender/pulls/128170
f095f41c4a