Support PostgreSQL 19

[wolfgangwalther]

Currently fails to build with compile error with PostgreSQL 19 beta 1.

[devrimgunduz]

Submitted a PR for that: #165

Per: pgdg-packaging/pgdg-rpms#213

[yugo-n]

I merged #170. Thanks!

I'll also add a fix to prohibit SQL/PGQ queries in view definitions and improve test stability on PG19.