feat(validation): add input validation for Bilateral and Blma constructors; enhance Butter and Mgdi calculations with NaN handling

lib/trends/ema/Ema.Tests.cs

@@ -551,6 +551,17 @@ public class EmaTests
         Assert.Equal(verifyEma.Last.Value, ema.Last.Value, 1e-10);
     }
 
+    [Fact]
+    public void Prime_AllNaNs_ReturnsNaN()
+    {
+        var ema = new Ema(5);
+        double[] history = [double.NaN, double.NaN, double.NaN];
+        
+        ema.Prime(history);
+        
+        Assert.True(double.IsNaN(ema.Last.Value));
+    }
+
     [Fact]
     public void Calculate_ReturnsCorrectResultsAndHotIndicator()
     {

lib/trends/ema/Ema.cs

@@ -118,15 +118,25 @@ public sealed class Ema : AbstractBase
         int i = 0;
 
         // Find first valid value to seed lastValid
+        bool foundValid = false;
         for (int k = 0; k < len; k++)
         {
             if (double.IsFinite(source[k]))
             {
                 _lastValidValue = source[k];
+                foundValid = true;
                 break;
             }
         }
 
+        if (!foundValid)
+        {
+            Last = new TValue(DateTime.MinValue, double.NaN);
+            _p_state = _state;
+            _p_lastValidValue = _lastValidValue;
+            return;
+        }
+
         if (!_state.IsCompensated)
         {
             for (; i < len && _state.E > COMPENSATOR_THRESHOLD; i++)