fn flush_to_batcher<T, O>(
updates: &mut Vec<(UpsertKey, T, UpsertDiff<O>)>,
chunker: &mut ColumnChunker<(UpsertKey, T, UpsertDiff<O>)>,
batcher: &mut ColumnMergeBatcher<UpsertKey, T, UpsertDiff<O>>,
)Expand description
Consolidate updates through chunker into Column chunks and push them
into batcher, emptying updates (keeping its capacity). The chunker
readies a fully-consolidated chunk per push_into, so the extract loop
drains everything it produced.