fix: udf name and pg_is_table_visible

[sunng87]

Fixes residual issues introduced in #112

\dt from psql finally returns no error. I will debug it further to make it return correct results.

[sunng87]

datafusion=> select * from pg_catalog.pg_namespace;
 oid  |      nspname       | nspowner | nspacl | options
------+--------------------+----------+--------+---------
   11 | pg_catalog         |       10 |        |
 2200 | public             |       10 |        |
   12 | information_schema |       10 |        |
(3 rows)

datafusion=> select relnamespace, relname from pg_catalog.pg_class;
 relnamespace |      relname
--------------+-------------------
        10000 | pg_type
        10000 | pg_class
        10000 | pg_attribute
        10000 | pg_namespace
        10000 | pg_proc
        10000 | pg_database
        10000 | pg_am
        10000 | pg_range
        10000 | pg_enum
        10010 | player_valuations
        10010 | clubs
        10010 | competitions
        10010 | games
        10010 | transfers
        10010 | game_lineups
        10010 | appearances
        10010 | players
        10010 | game_events
        10010 | club_games
(19 rows)

We just need to make sure the oid mapping is correct and consistent between pg_class and pg_namespace. This requires some state maintained between pg_catalog calls. I will address this later.