fix(ast): fix VALUES clause formatting to output multiple rows

The VALUES clause was incorrectly formatting multiple rows as a single
row with multiple columns. For example:
  VALUES ('A'), ('B'), ('C')
was being formatted as:
  VALUES ('A', 'B', 'C')

This caused the star expander to think the VALUES table had 3 columns
instead of 1, resulting in incorrect SELECT * expansion.

The fix properly iterates over each row in ValuesLists and wraps each
in parentheses.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: kyleconroy

internal/endtoend/testdata/accurate_cte_values/postgresql/stdlib/go/query.sql.go

@@ -37,9 +37,16 @@ func (n *SelectStmt) Format(buf *TrackedBuffer, d format.Dialect) {
 	}
 
 	if items(n.ValuesLists) {
-		buf.WriteString("VALUES (")
-		buf.astFormat(n.ValuesLists, d)
-		buf.WriteString(")")
+		buf.WriteString("VALUES ")
+		// ValuesLists is a list of rows, where each row is a List of values
+		for i, row := range n.ValuesLists.Items {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			buf.WriteString("(")
+			buf.astFormat(row, d)
+			buf.WriteString(")")
+		}
 		return
 	}