Add Kahan-Babuška Summation Algorithm and Enhance Variance Indicator Tests

- Introduced a new `Sum` class implementing the Kahan-Babuška algorithm for high-precision rolling summation.
- Added comprehensive documentation for the `Sum` class, detailing its mathematical foundation, performance profile, and use cases.
- Refactored `VarianceIndicator` tests to improve clarity and coverage, including checks for different source types and the ability to change properties.
- Enhanced `UsfIndicator` tests to validate initialization, processing of updates, and property changes.
- Updated `UsfIndicator` implementation to simplify source handling and improve short name generation.
- Modified Qodana configuration to exclude unused auto property accessor warnings.

lib/statistics/sum/Sum.Quantower.cs

@@ -0,0 +1,55 @@
+using System.Drawing;
+using System.Runtime.CompilerServices;
+using TradingPlatform.BusinessLayer;
+
+namespace QuanTAlib;
+
+[SkipLocalsInit]
+public sealed class SumIndicator : Indicator, IWatchlistIndicator
+{
+    [InputParameter("Period", sortIndex: 0, minimum: 1, maximum: 10000)]
+    public int Period { get; set; } = 14;
+
+    [IndicatorExtensions.DataSourceInput]
+    public SourceType Source { get; set; } = SourceType.Close;
+
+    [InputParameter("Show cold values", sortIndex: 21)]
+    public bool ShowColdValues { get; set; } = true;
+
+    private Sum? _sum;
+    private readonly LineSeries? _series;
+    private string? _sourceName;
+    private Func<IHistoryItem, double>? _priceSelector;
+
+    public static int MinHistoryDepths => 0;
+    int IWatchlistIndicator.MinHistoryDepths => MinHistoryDepths;
+
+    public override string ShortName => $"SUM({Period}):{_sourceName}";
+
+    public SumIndicator()
+    {
+        OnBackGround = true;
+        SeparateWindow = true;
+        Name = "SUM - Rolling Sum";
+        Description = "Rolling Sum with Kahan-Babuška summation for numerical stability";
+        _series = new(name: "SUM", color: IndicatorExtensions.Statistics, width: 2, style: LineStyle.Solid);
+        AddLineSeries(_series);
+    }
+
+    protected override void OnInit()
+    {
+        _priceSelector = Source.GetPriceSelector();
+        _sourceName = Source.ToString();
+        _sum = new Sum(Period);
+        base.OnInit();
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    protected override void OnUpdate(UpdateArgs args)
+    {
+        bool isNew = args.IsNewBar();
+        var item = HistoricalData[Count - 1, SeekOriginHistory.Begin];
+        double value = _sum!.Update(new TValue(item.TimeLeft.Ticks, _priceSelector!(item)), isNew).Value;
+        _series!.SetValue(value, _sum.IsHot, ShowColdValues);
+    }
+}