Add SETOF support for PostgreSQL function return types

[fmguerreiro]

PostgreSQL functions can return sets via RETURNS SETOF <type>. This is currently not supported by the parser, which fails when encountering SETOF after RETURNS.

Changes

• Add SETOF keyword
• Add DataType::SetOf(Box<DataType>) variant
• Handle SETOF in parse_data_type_helper() so any DataType::SetOf round-trips through Display → parse
• Tests for SETOF with TEXT, INTEGER, RECORD, and schema-qualified custom types

Example

CREATE FUNCTION get_users() RETURNS SETOF TEXT LANGUAGE sql AS 'SELECT name FROM users';
CREATE FUNCTION get_all() RETURNS SETOF my_schema."MyType" LANGUAGE sql AS 'SELECT * FROM t';

Reference

• PostgreSQL CREATE FUNCTION docs