Need profiling and performance regression tests

[bocajnotnef]

This would probably matter more when we get to our milestone, but it would be good if we monitored performance so we don't accidentally triple our runtime at some point.

Should be fairly simple: either subprocess 'time' a bunch of runs, or use python's own time profiling monitors; run a few hundred rounds of the preprocessor, take the average and assert it's below a certian range.

We could make it CI-only so it doesn't clog the normal make test call.