SortPreservingMerge Special Case Single Column

[tustvold]

Is your feature request related to a problem or challenge?

SortPreservingMerge currently always uses the arrow row format, this provides compelling benefits when sorting by a tuple of multiple columns. However, it is often the case that a sort is being performed on a single column. lexsort_to_indices which is used by SortExec detects this case and calls through to sort_to_indices which has specialised implementations for each column type. This significantly outperforms converting to the row format as it allows for fixed width comparisons, which are significantly faster

Describe the solution you'd like

I would like to be able to use a specialized, fixed width sort cursor within SortPreservingMerge

Describe alternatives you've considered

No response

Additional context

#5854 contained a POC implementation of this

[alamb]

cc @jaylmiller