Fresh oldest-first sum over each complete finite window; NaN on warmup or
overflow. Missing values expire with the window. Valid integer periods use
O(n * period) time and O(1) extra working storage, excluding the result.
Unsupported scalar periods retain their historical behavior.
Fresh oldest-first sum over each complete finite window; NaN on warmup or overflow. Missing values expire with the window. Valid integer periods use O(n * period) time and O(1) extra working storage, excluding the result. Unsupported scalar periods retain their historical behavior.