fn merge_merge_scan_region_watermarks(
merged: &mut BTreeMap<u64, MergeState>,
regions: impl IntoIterator<Item = u64>,
sub_stage_metrics: impl IntoIterator<Item = RecordBatchMetrics>,
)fn merge_merge_scan_region_watermarks(
merged: &mut BTreeMap<u64, MergeState>,
regions: impl IntoIterator<Item = u64>,
sub_stage_metrics: impl IntoIterator<Item = RecordBatchMetrics>,
)