Add Intraday Intensity Index (III) implementation and tests

- Implemented the III indicator in Iii.Quantower.cs, measuring buying/selling pressure based on close price within the day's range, weighted by volume.
- Added unit tests for III functionality in Iii.Tests.cs, covering various scenarios including default parameters, updates, and cumulative mode.
- Created validation tests in Iii.Validation.Tests.cs to ensure consistency between streaming, batch, and span calculations.
- Developed comprehensive documentation for III in Iii.md, detailing its historical context, mathematical foundation, and common pitfalls.

lib/volume/efi/Efi.Quantower.Tests.cs

@@ -0,0 +1,159 @@
+using TradingPlatform.BusinessLayer;
+
+namespace QuanTAlib.Tests;
+
+public class EfiIndicatorTests
+{
+    [Fact]
+    public void EfiIndicator_Constructor_SetsDefaults()
+    {
+        var indicator = new EfiIndicator();
+
+        Assert.Equal("EFI - Elder's Force Index", indicator.Name);
+        Assert.Equal(13, indicator.Period);
+        Assert.True(indicator.SeparateWindow);
+        Assert.True(indicator.OnBackGround);
+        Assert.Equal(13, indicator.MinHistoryDepths);
+    }
+
+    [Fact]
+    public void EfiIndicator_ShortName_ReflectsPeriod()
+    {
+        var indicator = new EfiIndicator { Period = 20 };
+        Assert.Equal("EFI(20)", indicator.ShortName);
+    }
+
+    [Fact]
+    public void EfiIndicator_MinHistoryDepths_EqualsPeriod()
+    {
+        var indicator = new EfiIndicator { Period = 26 };
+
+        Assert.Equal(26, indicator.MinHistoryDepths);
+        Assert.Equal(26, ((IWatchlistIndicator)indicator).MinHistoryDepths);
+    }
+
+    [Fact]
+    public void EfiIndicator_Initialize_CreatesInternalEfi()
+    {
+        var indicator = new EfiIndicator();
+
+        // Initialize should not throw
+        indicator.Initialize();
+
+        // After init, line series should exist
+        Assert.Single(indicator.LinesSeries);
+    }
+
+    [Fact]
+    public void EfiIndicator_ProcessUpdate_HistoricalBar_ComputesValue()
+    {
+        var indicator = new EfiIndicator();
+        indicator.Initialize();
+
+        // Add historical data
+        var now = DateTime.UtcNow;
+        for (int i = 0; i < 30; i++)
+        {
+            indicator.HistoricalData.AddBar(now.AddMinutes(i), 100 + i, 110 + i, 90 + i, 105 + i, 1000 + (i * 100));
+
+            // Process update for each bar to simulate history loading
+            var args = new UpdateArgs(UpdateReason.HistoricalBar);
+            indicator.ProcessUpdate(args);
+        }
+
+        // Line series should have a value
+        double val = indicator.LinesSeries[0].GetValue(0);
+        Assert.True(double.IsFinite(val));
+    }
+
+    [Fact]
+    public void EfiIndicator_ProcessUpdate_NewBar_ComputesValue()
+    {
+        var indicator = new EfiIndicator();
+        indicator.Initialize();
+
+        var now = DateTime.UtcNow;
+        for (int i = 0; i < 30; i++)
+        {
+            indicator.HistoricalData.AddBar(now.AddMinutes(i), 100 + i, 110 + i, 90 + i, 105 + i, 1000 + (i * 100));
+        }
+
+        indicator.ProcessUpdate(new UpdateArgs(UpdateReason.HistoricalBar));
+
+        // Add new bar
+        indicator.HistoricalData.AddBar(now.AddMinutes(30), 130, 140, 120, 135, 1500);
+        indicator.ProcessUpdate(new UpdateArgs(UpdateReason.NewBar));
+
+        Assert.Equal(2, indicator.LinesSeries[0].Count);
+    }
+
+    [Fact]
+    public void EfiIndicator_Value_IsFinite()
+    {
+        var indicator = new EfiIndicator();
+        indicator.Initialize();
+
+        var now = DateTime.UtcNow;
+        for (int i = 0; i < 50; i++)
+        {
+            // Create varying price patterns
+            double open = 100 + i;
+            double high = open + 10 + (i % 5);
+            double low = open - 5;
+            double close = (i % 2 == 0) ? high - 1 : low + 1; // Alternate high/low closes
+            double volume = 1000 + (i * 100);
+
+            indicator.HistoricalData.AddBar(now.AddMinutes(i), open, high, low, close, volume);
+            indicator.ProcessUpdate(new UpdateArgs(UpdateReason.HistoricalBar));
+        }
+
+        double val = indicator.LinesSeries[0].GetValue(0);
+        Assert.True(double.IsFinite(val), $"EFI value {val} should be finite");
+    }
+
+    [Fact]
+    public void EfiIndicator_PositiveForce_OnPriceIncrease()
+    {
+        var indicator = new EfiIndicator { Period = 3 };
+        indicator.Initialize();
+
+        var now = DateTime.UtcNow;
+
+        // First bar: baseline
+        indicator.HistoricalData.AddBar(now, 100, 105, 95, 100, 1000);
+        indicator.ProcessUpdate(new UpdateArgs(UpdateReason.HistoricalBar));
+
+        // Add bars with increasing prices and high volume
+        for (int i = 1; i <= 10; i++)
+        {
+            indicator.HistoricalData.AddBar(now.AddMinutes(i), 100 + (i * 5), 110 + (i * 5), 95 + (i * 5), 105 + (i * 5), 5000);
+            indicator.ProcessUpdate(new UpdateArgs(UpdateReason.HistoricalBar));
+        }
+
+        double val = indicator.LinesSeries[0].GetValue(0);
+        Assert.True(val > 0, $"EFI should be positive on sustained price increase, got {val}");
+    }
+
+    [Fact]
+    public void EfiIndicator_NegativeForce_OnPriceDecrease()
+    {
+        var indicator = new EfiIndicator { Period = 3 };
+        indicator.Initialize();
+
+        var now = DateTime.UtcNow;
+
+        // First bar: baseline
+        indicator.HistoricalData.AddBar(now, 150, 155, 145, 150, 1000);
+        indicator.ProcessUpdate(new UpdateArgs(UpdateReason.HistoricalBar));
+
+        // Add bars with decreasing prices and high volume
+        for (int i = 1; i <= 10; i++)
+        {
+            indicator.HistoricalData.AddBar(now.AddMinutes(i), 150 - (i * 5), 155 - (i * 5), 145 - (i * 5), 145 - (i * 5), 5000);
+            indicator.ProcessUpdate(new UpdateArgs(UpdateReason.HistoricalBar));
+        }
+
+        double val = indicator.LinesSeries[0].GetValue(0);
+        Assert.True(val < 0, $"EFI should be negative on sustained price decrease, got {val}");
+    }
+}