sketch_sliding_window.nx

sketch_sliding_window.nx -- last-W-samples rolling aggregator. Circular buffer of size W with running sum + lazy min/max tracking. Useful for "last 5 minutes / last 100 events" rolling computations when the EXACT window is required (vs EWMA's exponential decay). AGGREGATES MAINTAINED: sum -- running sum (O(1) update) count -- min(window_size, observations) — useful at warm-up min -- minimum (lazy: recompute via full scan when displaced) max -- maximum (lazy: same) USE CASES: - SRE: last-5-minute p99 latency window - finance: 20-period moving average - sensor: rolling-window anomaly thresholds - rate-limiting: requests per fixed window MIN/MAX LAZY STRATEGY: cheaper than monotonic-deque for typical W. Cached min/max valid until the displaced sample equaled the cached value; then we rescan the buffer. Worst-case O(W) on eviction, O(1) amortized for "no extremum eviction." For deterministic O(1)-per-op monotonic-deque variant, swap in v2.