What has been pointed out from the README; also: - Separation of concerns, since with a single external process we can share object store caches without compli

What has been pointed out from the README; also: - Separation of concerns, since with a single external process we can share object store caches without complicated locking dances between multiple processes. - Memory limits are easier to reason about with a single external process. - Postgres backends end up being more robust, as you can restart the pgduck_server process separately.