Fixes #55: Correct the order of the columns returned by pgmq_read() and pgmq_pop().

[rzavalet]

The result set columns of pgmq_send() and pgmq_pop() is currently inconsistent with the order of columns in the underlying queue table (See Issue #55). This PR makes the order consistent.

Sample output for pgmq_send():

testdb=# select * from pgmq_send('my_queue', '{"foo": "bar1"}');
 pgmq_send 
-----------
         1
(1 row)

testdb=# select * from pgmq_send('my_queue', '{"foo": "bar2"}');
 pgmq_send 
-----------
         2
(1 row)

testdb=# select * from pgmq_read('my_queue', 30, 2);
 msg_id | read_ct |          enqueued_at          |              vt               |     message     
--------+---------+-------------------------------+-------------------------------+-----------------
      1 |       1 | 2023-08-15 22:59:54.335146-06 | 2023-08-15 23:00:47.513264-06 | {"foo": "bar1"}
      2 |       1 | 2023-08-15 23:00:04.972114-06 | 2023-08-15 23:00:47.513264-06 | {"foo": "bar2"}
(2 rows)

testdb=# select * from pgmq_my_queue;
 msg_id | read_ct |          enqueued_at          |              vt               |     message     
--------+---------+-------------------------------+-------------------------------+-----------------
      1 |       1 | 2023-08-15 22:59:54.335146-06 | 2023-08-15 23:00:47.513264-06 | {"foo": "bar1"}
      2 |       1 | 2023-08-15 23:00:04.972114-06 | 2023-08-15 23:00:47.513264-06 | {"foo": "bar2"}
(2 rows)

Sample output for pgmq_pop():

testdb=# select * from pgmq_send('my_queue', '{"foo": "bar3"}');
 pgmq_send 
-----------
         3
(1 row)

testdb=# select * from pgmq_pop('my_queue');
 msg_id | read_ct |          enqueued_at          |              vt               |     message     
--------+---------+-------------------------------+-------------------------------+-----------------
      3 |       0 | 2023-08-15 23:00:37.947369-06 | 2023-08-15 23:00:37.947369-06 | {"foo": "bar3"}
(1 row)

I verified that the following tests still pass:

> cargo test
    Finished test [unoptimized + debuginfo] target(s) in 0.10s
     Running unittests src/lib.rs (target/debug/deps/pgmq-c90b88e7628f9490)

running 7 tests
    Building extension with features pg_test pg15
     Running command "/home/rzavalet/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/cargo" "build" "--features" "pg_test pg15" "--no-default-features" "--message-format=json-render-diagnostics"
  Installing extension
     Copying control file to /opt/postgres/share/extension/pgmq.control
     Copying shared library to /opt/postgres/lib/pgmq.so
     Copying extension schema upgrade file to /opt/postgres/share/extension/pgmq--0.7.4--0.7.5.sql
     Copying extension schema upgrade file to /opt/postgres/share/extension/pgmq--0.11.1--0.11.2.sql
     Copying extension schema upgrade file to /opt/postgres/share/extension/pgmq--0.7.3--0.7.4.sql
     Copying extension schema upgrade file to /opt/postgres/share/extension/pgmq--0.7.5--0.8.0.sql
     Copying extension schema upgrade file to /opt/postgres/share/extension/pgmq--0.8.0--0.8.1.sql
    Finished installing pgmq
test tests::pg_test_validate_same_type ... ok
test partition::tests::pg_test_map_partition_col ... ok
test tests::pg_test_internal ... ok
test tests::pg_test_default ... ok
test tests::pg_test_creat_non_partitioned ... ok
test tests::pg_test_archive ... ok
test tests::pg_test_partitioned ... ok

test result: ok. 7 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 3.39s

stopping postgres (pid=273762)
     Running tests/integration_tests.rs (target/debug/deps/integration_tests-2cedb8858eeabbb1)

running 1 test
test test_lifecycle ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.63s

Let me know if I should test something else.

[ChuckHend]

All the tests passed in CI too. Thank you for helping!

[ChuckHend]

closes #55