feat: support calling PostgreSQL procedures with the macros

Fixes #1449 (I think). I verified that the code fixes the new test.

I used INOUT in setup.sql because older versions of Postgres don't
support OUT parameters.

tests/postgres/setup.sql

@@ -41,3 +41,6 @@ CREATE TABLE products (
     name TEXT,
     price NUMERIC CHECK (price > 0)
 );
+
+CREATE OR REPLACE PROCEDURE forty_two(INOUT forty_two INT = NULL)
+    LANGUAGE plpgsql AS 'begin forty_two := 42; end;';