request mode: window union over (last join) expect wrong schema of union query

In request mode, `window union over (t1 last join t2) ` , the union query expect a schema of t1 (left query), it should be `t1 + t2` instead

The issue is about a window union query in request mode expecting the wrong schema. Look at the SQL parser and query planner for window union operations, especially around 'last join'. Check the schema inference logic for union queries in request mode. The fix likely involves updating the schema combination logic to include columns from both t1 and t2.

Written by the indexing model from the issue text.