Fuzzing using SQLsmith

Once we're unable to crash postgres easily ourselves we should use [SQLsmith](https://github.com/anse1/sqlsmith) to run a bunch of randomly generated queries. If these cause errors or don't work, that's "fine" but they shouldn't be causing crashes.

Start by reviewing how this C++ project currently executes PostgreSQL queries and where crashes can be detected; the issue names no files or tests. Evaluate integrating SQLsmith to generate randomized queries, and consider the work done when those queries no longer cause crashes, even if they produce errors or fail otherwise.

Written by the indexing model from the issue text.