Realtime LineChart poor performance due to calcMinMax

I've found a possible performance bottleneck. In a realtime chart Adding many entries per second to the chart I noticed that automatically the calcMinMax of the dataset is called just after EACH values.append(e)

calcMinMax function determine the min and max values using .forEach that is causing the CPU over 60% spent looping the values, moreover in the main thread.

I'm performing some experiment disabling min/max calculation or using native for loop instead of array .forEach

@danielgindi please have a look, is really calcMinMax on all values needed? I calculate min/max Y values manually in my code and only on visible values, so maybe you could expose some boolean to enable/disable min/max auto calculation and improving performance removing the forEach function and avoid function calls.

```
open override func calcMinMax()
{
    guard !values.isEmpty else { return }

    _yMax = -Double.greatestFiniteMagnitude
    _yMin = Double.greatestFiniteMagnitude
    _xMax = -Double.greatestFiniteMagnitude
    _xMin = Double.greatestFiniteMagnitude

    values.forEach { calcMinMax(entry: $0) }
}