Decorrelate a window function below a correlated equality filter by extending PARTITION BY #25897

Follow-up to #25838 and #25792.

PullUpCorrelatedExpr now pulls a correlated filter above a Window only when the filter reads plain PARTITION BY columns. Any other correlated filter below a window keeps the subquery correlated, and the query fails with "Physical plan does not support logical expression …". For example (#25792):

SELECT t1.id, sub.id, sub.rn
FROM t1, LATERAL (
    SELECT t2.id, row_number() OVER (ORDER BY t2.id) AS rn
    FROM (SELECT * FROM t2 WHERE t2.t1_id = t1.id) AS t2
) AS sub;

Proposal: when every correlated conjunct below the window has the form inner_col = <outer expr>, it fixes inner_col for each outer row. We can then add inner_col to the PARTITION BY of every window function and pull the filter above the window. Spark (DecorrelateInnerQuery, Window case) and DuckDB (FlattenDependentJoins::PushDownWindow) do this. A Projection on top restores the original window column names.

Caveats:

• Only a plain column equality qualifies. can_pullup_over_aggregation also accepts CAST(col AS …) = outer, and a lossy cast would map several col values to one outer row, so partitioning by col would give wrong results.
• Skip it when the window's input needs the count-bug handling.