fix: paren data source

[psteinroe]

fixes data sources within parentheses. they can be either

• a select statement
• a join clause

this is now parsed properly:

select f1, count(*) from
  t1 x(x0,x1) left join (t1 left join t2 using(f1)) on (x0 = 0)

also uses column_list instead of tuple_expr for join using (…) nodes.

and added a little comment to the regression test to track how many are still failing.

[netlify]

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Name	Link
🔨 Latest commit	a0b1d25

[sbdchd]

Thank you!