fix: allow cast to type with column alias in postgres

[hellozimi]

The issue I experienced with the postgresql parser was that the following query did not resolve the column alias for the "createdAt" column which was casted - it resolved to null. The count(*) "value" did however resolve correctly to its alias.

select "createdAt"::date as "date",
  count(*) as "value"
  from object_event_log
  group by "createdAt"::date

The solution was to remove the alias:alias_clause? from the cast_double_colon rule, since the alias should be handled at the column_list_item level where the cast expression is used.