interpret: copy_provenance: avoid large intermediate buffer for large repeat counts
Copying provenance worked in this odd way where the "preparation" phase (which is supposed to just extract the necessary information from the source range) already did all the work of repeating the result N times for the target range. This was needed to use the existing `insert_presorted` function on `SortedMap`.
This PR generalizes `insert_presorted` so that we can avoid this odd structure on copy-provenance, and maybe even improve performance.
5d1b897a07