* feat: add function 'pg_catalog.pg_table_is_visible'q
* feat: add 'pg_class' and 'pg_namespace', now we can run '\d' and '\dt'!
* refactor: move memory_table::tables to utils::tables
* refactor: move out predicate to system_schema to reuse it
* feat: predicates pushdown
* test: add pg_namespace, pg_class related sqlness test
* fix: typos and license header
* fix: sqlness test
* refactor: use `expect` instead of `unwrap` here
* refactor: remove the `information_schema::utils` mod
* doc: make the comment in pg_get_userbyid more precise
* doc: add TODO and comment in pg_catalog
* fix: typo
* fix: sqlness
* doc: change to comment on PGClassBuilder to TODO
* WIP: pg_catalog
* refactor: move memory_table to crate public level to reuse it in pgcatalog
* refactor: new system_schema mod to manage implementation of information_schema and pg_catalog
* feat: pg_catalog.pg_type
* fix: remove unused code to avoid warning
* test: add pg_catalog sqlness test
* feat: pg_catalog_cache in system_catalog
* fix: integration test
* test: rollback unit test
* refactor: mix pg_catalog table_id with old ones
* fix: add todo information
* tests: rerun sqlness
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Co-authored-by: johnsonlee <johnsonlee@localhost.localdomain>
