using NewThreadSafeMovingAverage by default is overhead

NewThreadSafeMovingAverage wrapper isn't needed unless decorator relying on
ewma.MovingAverage is shared among multiple bars. If there is need to share
a decorator, NewThreadSafeMovingAverage must be used explicitly.

decor/eta.go

@@ -39,7 +39,7 @@ func EwmaETA(style TimeStyle, age float64, wcc ...WC) Decorator {
 	} else {
 		average = ewma.NewMovingAverage(age)
 	}
-	return MovingAverageETA(style, NewThreadSafeMovingAverage(average), nil, wcc...)
+	return MovingAverageETA(style, average, nil, wcc...)
 }
 
 // MovingAverageETA decorator relies on MovingAverage implementation to calculate its average.

decor/moving_average.go

@@ -70,5 +70,5 @@ func (s *medianWindow) Set(value float64) {
 
 // NewMedian is fixed last 3 samples median MovingAverage.
 func NewMedian() ewma.MovingAverage {
-	return NewThreadSafeMovingAverage(new(medianWindow))
+	return new(medianWindow)
 }

decor/speed.go

@@ -46,7 +46,7 @@ func EwmaSpeed(unit interface{}, format string, age float64, wcc ...WC) Decorato
 	} else {
 		average = ewma.NewMovingAverage(age)
 	}
-	return MovingAverageSpeed(unit, format, NewThreadSafeMovingAverage(average), wcc...)
+	return MovingAverageSpeed(unit, format, average, wcc...)
 }
 
 // MovingAverageSpeed decorator relies on MovingAverage implementation