I'm now at the point where I can successfully run our entire application test suite, not just the stdlib ones. Here's how much the database grows in each version:
cSuneido: 20 mb
immudb1: 400 mb :-(
immudb2: 19 mb :-)
I'm happy that my decision to back up and try a different approach turned out to be a good one.
It's not too surprising that immudb2 gives slightly better results than cSuneido for running tests, since it will often avoid persisting indexes for temporary tables, whereas cSuneido will always write them.
NOTE: This is still not a realistic workload. I suspect immudb will end up having more database growth than cSuneido. But as long as it's not excessive (as these results would tend to indicate) then it's ok.