fix(query): preserve parentheses in UNION queries

[sundy-li]

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Summary

This PR fixes issue #19578 where SQL parser assertions fail when parsing UNION expressions with parentheses.

Problem: When parsing SQL with parentheses around UNION expressions (e.g., SELECT 1 UNION (SELECT 1 UNION SELECT 1 UNION SELECT 1)), the parentheses were lost during AST conversion, causing panics in assert_reparse when trying to display the query.

Root Cause: In src/query/ast/src/parser/query.rs, the SetOperationParser::primary() method directly returned SetOperationElement::Group(expr) as expr, losing the parentheses information.

Solution: Modified SetOperationParser::primary method to properly wrap grouped expressions as SetExpr::Query.

Changes:

• Changed SetOperationElement::Group(expr) => expr to:

  SetOperationElement::Group(expr) => {
      let mut query = expr.into_query();
      query.span = transform_span(input.span.tokens);
      SetExpr::Query(Box::new(query))
  }

• This ensures parentheses are preserved when converting AST back to SQL

• fixes: parse assertion failed #19578

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Testing: All UNION expressions with parentheses now parse and serialize correctly:

• SELECT 1 UNION (SELECT 1 UNION SELECT 1 UNION SELECT 1) - original issue
• SELECT 1 UNION (SELECT 2)
• (SELECT 1) UNION SELECT 2
• Other UNION/INTERSECT/EXCEPT combinations with parentheses

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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