I haven't had time to try it, but I thought running PG on a copy-on-write filesystem with a specific "clone template" incantation would get you instant clones? Probably doable in a docker container? https://boringsql.com/posts/instant-database-clones/

Possibly — but then you need a cowfs everywhere you run your tests. Templates are already really fast. Give it a shot and lmk if it’s faster!