SQL Parser
BigQuery QUALIFY conditions are represented by query.Select.QualifyClause.
The existing query.Select.Qualify field continues to represent WHERE.
Inline window expressions use expr.Window, including PARTITION BY,
ORDER BY, and ROWS/RANGE frames with integer or placeholder offsets.
Named window declarations and references (WINDOW w AS (...), OVER w)
are not supported.
Traversal includes window expressions, QUALIFY conditions, parsed CTEs, and
derived tables. Window results are computed expressions rather than direct
scalar-column lineage. Stringifier{PreserveWindow: true} retains LIMIT/OFFSET
as before; inline OVER specifications and QUALIFY are always rendered.