Function evaluate_window_batch 

pub fn evaluate_window_batch(
    func: &WindowFunction,
    spec: &WindowSpec,
    target_column: usize,
    batch: &RecordBatch,
) -> Result<Vec<Value>>

Evaluate a window function directly over a RecordBatch.

This is a convenience wrapper around evaluate_window that extracts values from columns exactly the way crate::executor::filter does. Column indices in spec and target_column are positions into batch.columns.