…_statements

closes #2622

refs:
* https://serde.rs/enum-representations.html#untagged
* https://serde.rs/field-attrs.html#skip
* https://www.postgresql.org/docs/current/pgstatstatements.html
  * https://www.postgresql.org/docs/current/runtime-config-statistics.html#GUC-COMPUTE-QUERY-ID

```
error: error occurred while decoding column 0: data did not match any variant of untagged enum Explain at line 3 column 1
Error:    --> tests/postgres/macros.rs:103:15
    |
103 |     let row = sqlx::query!(r#"CALL forty_two(null)"#)
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: this error originates in the macro `$crate::sqlx_macros::expand_query` which comes from the expansion of the macro `sqlx::query` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `sqlx` (test "postgres-macros") due to previous error
```