feat(tests): add comprehensive tests for LinReg, StdDev, Variance, and Mama indicators; enhance Pwma constructor with null check; improve coverage path mappings in Qodana configuration

lib/trends/pwma/Pwma.Tests.cs

@@ -8,6 +8,7 @@ public class PwmaTests
     {
         Assert.Throws<ArgumentException>(() => new Pwma(0));
         Assert.Throws<ArgumentException>(() => new Pwma(-1));
+        Assert.Throws<ArgumentNullException>(() => new Pwma(null!, 10));
 
         var pwma = new Pwma(10);
         Assert.NotNull(pwma);

lib/trends/pwma/Pwma.cs

@@ -56,6 +56,7 @@ public sealed class Pwma : AbstractBase
 
     public Pwma(ITValuePublisher source, int period) : this(period)
     {
+        if (source == null) throw new ArgumentNullException(nameof(source));
         source.Pub += (item) => Update(item);
     }