Implement Multi Query support in V3 Branch

[mattbucci]

WPDB driver does not use multiquery so I haven't implemented it.

Since PostgreSQL does not have a built-in PHP function that directly mimics mysqli_more_results(), you would manage multi-statement transaction control differently.

In PostgreSQL, you can execute multiple statements with a single call to pg_query(), but you will get back only the result of the last statement. To execute multiple statements and handle them individually, you would typically use multiple calls to pg_query()

flush() specifically calls the functions wpsqli_more_results and wpsqli_next_result which I've currently just set to return false

https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/blob/bf2ef7f4185d5327543ded7df42efb16ff79fa7c/pg4wp/driver_pgsql.php#L521C1-L545C2

/**
 * Executes one or multiple queries which are concatenated by a semicolon.
 *
 * This function is a wrapper for the pg_multi_query function. It allows execution of
 * multiple SQL statements sent to the PostgreSQL server in a single call. This can be useful to
 * perform a batch of SQL operations such as an atomic transaction that should either complete
 * entirely or not at all. After calling this function, the results of the queries can be
 * processed using pg_store_result() and pg_next_result(). It is important to ensure
 * that any user input included in the queries is properly sanitized to avoid SQL injection.
 *
 * @param PgSql\Connection $connection The pg connection resource.
 * @param string $query The queries to execute, concatenated by semicolons.
 * @return bool Returns TRUE on success or FALSE on the first error that occurred.
 *              If the first query succeeds, the function will return TRUE even if
 *              a subsequent query fails.
 */
function wpsqli_multi_query(&$connection, $query)
{
    // Store the initial SQL query
    $initial = $query;
    // Rewrite the SQL query for compatibility with Postgres
    $sql = pg4wp_rewrite($query);
    throw new \Exception("PG4WP: Not Yet Implemented");
    // mysqli_multi_query => No direct equivalent. Multiple queries must be executed separately in PostgreSQL.
}

https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/blob/bf2ef7f4185d5327543ded7df42efb16ff79fa7c/pg4wp/driver_pgsql.php#L989

/**
 * Checks if there are any more result sets from a multi query.
 *
 * mysqli_more_results => No direct equivalent in PostgreSQL.
 * PostgreSQL does not support multiple results like MySQL's multi_query function.
 * It returns TRUE if one or more result sets are available from the previous calls to
 * pg_multi_query(), otherwise FALSE.
 *
 * @param PgSql\Connection $connection The pg connection resource.
 * @return bool Returns TRUE if there are more result sets from previous multi queries and
 *              FALSE otherwise.
 */
function wpsqli_more_results(&$connection)
{
    // mysqli_more_results => No direct equivalent in PostgreSQL.
    // PostgreSQL does not have a built-in function to check for more results from a batch of queries.
    return false;
}

https://github.com/PostgreSQL-For-Wordpress/postgresql-for-wordpress/blob/bf2ef7f4185d5327543ded7df42efb16ff79fa7c/pg4wp/driver_pgsql.php#L1006

/**
 * Moves the internal result pointer to the next result set returned from a multi query.
 *
 * mysqli_next_result => No direct equivalent in PostgreSQL.
 * PostgreSQL does not support multiple results like MySQL's multi_query function.
 * FALSE if there are no more result sets, or FALSE with an error if there is a problem moving the result pointer.
 *
 * @param PgSql\Connection $connection The pg connection resource.
 * @return bool Returns TRUE on success or FALSE on failure (no more results or an error occurred).
 */
function wpsqli_next_result(&$connection)
{
    // mysqli_next_result => No direct equivalent in PostgreSQL.
    // PostgreSQL does not support multiple results like MySQL's multi_query function.
    return false;
}