Function sma

Simple moving average. Valid scalar windows without options sum oldest first afresh, then divide once. Missing or overflowing sums produce NaN and recover when they expire. This uses O(n * period) time and O(1) extra working storage. Unsupported scalar periods retain their historical behavior. Supplied skip collects period finite observations and holds across gaps; propagate (also the default for {}) requires a complete chronological window. Warmup is NaN. Option-path periods must be positive safe integers; invalid periods throw RangeError and malformed options throw TypeError.

Bar-aligned lengths use each current window; NaN lengths give gaps. Arrays default to propagation.