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/macros.rs

@@ -96,6 +96,19 @@ async fn test_void() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[sqlx_macros::test]
+async fn test_call_procedure() -> anyhow::Result<()> {
+    let mut conn = new::<Postgres>().await?;
+
+    let row = sqlx::query!(r#"CALL forty_two(null)"#)
+        .fetch_one(&mut conn)
+        .await?;
+
+    assert_eq!(row.forty_two, Some(42));
+
+    Ok(())
+}
+
 #[sqlx_macros::test]
 async fn test_query_file() -> anyhow::Result<()> {
     let mut conn = new::<Postgres>().await?;

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;';