Improve postgres CREATE FUNCTION support

Hey,

I'm trying to parse `CREATE FUNCTION` statements (PostgreSQL) with the following attributes:

```sql
CREATE OR REPLACE FUNCTION public.accounting_ids()
RETURNS SETOF uuid
LANGUAGE plpgsql
STABLE SECURITY DEFINER
SET search_path TO ''
AS $function$
```

A few features fail to parse:
1. `SETOF [type]` is not supported (Expected: end of statement, found: uuid at Line: 5, Column: 16)
2. `SECURITY DEFINER` is not supported (Expected: end of statement, found: SECURITY at Line: 7, Column: 9)
3. `SET search_path TO ''` is not supported (Expected: end of statement, found: SET at Line: 7, Column: 2)

Using sqlparser 0.50.0

Reproduce the PostgreSQL CREATE FUNCTION example against sqlparser 0.50.0 and locate the parser entry point for CREATE FUNCTION. Trace how return types and function attributes are handled, then add coverage for SETOF uuid, SECURITY DEFINER, and SET search_path TO ''. Done means all three constructs parse successfully.

Written by the indexing model from the issue text.