See if batching timeline updates can further reduce scroll jumps

[bwindels]

My intuition tells me it might, having looked at profiling data. Also, after having cleared the indexeddb, it seems to jump less, wonder if I'm imagining things 👀

The idea would be to either:

• add proper batching to observable collections
• auto batch in list view and as long as operations are homogeneous (same type, continuous range), keep expanding the batch, and close it with an rAF.

The latter would be easier.