Refactor error handling and calculations in TheilU, Wmape, and TukeyBiweight classes; update buffer handling for consistency

- Updated buffer handling in TheilU and Wmape classes to ensure consistency after adding new values.
- Changed the resync interval constant in TukeyBiweight for better clarity.
- Refactored state structures to record structs in Gauss, Hann, Hp, Hpf, Kalman, Loess, Notch, and other filter classes for improved performance and readability.
- Enhanced numerical stability in Mama class calculations using Fused Multiply-Add (FMA) for precision.
- Added comprehensive tests for Atan2 validation to compare .NET's Math.Atan2 with PineScript's implementation, ensuring accuracy across various edge cases.
- Updated NDepend badges to reflect changes in classes, methods, and lines of code.

lib/filters/gauss/Gauss.cs

@@ -25,13 +25,11 @@ public sealed class Gauss : AbstractBase
     private State _p_state;
 
     [StructLayout(LayoutKind.Auto)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct State
+    private record struct State
     {
         public double LastValue;
         public bool IsHot;
     }
-    #pragma warning restore CA1066
 
     /// <summary>
     /// Gets the kernel size used for the filter.

lib/filters/hann/Hann.cs

@@ -20,13 +20,11 @@ public sealed class Hann : AbstractBase
     private State _p_state;
 
     [StructLayout(LayoutKind.Auto)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct State
+    private record struct State
     {
         public double LastValue;
         public bool IsHot;
     }
-    #pragma warning restore CA1066
 
     /// <summary>
     /// Gets the length of the window (period).

lib/filters/hp/Hp.cs

@@ -25,15 +25,13 @@ public sealed class Hp : AbstractBase
     private State _p_state;
 
     [StructLayout(LayoutKind.Auto)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct State
+    private record struct State
     {
         public double Trend;
         public double PrevTrend;
         public double PrevPrice;
         public bool IsInitialized;
     }
-    #pragma warning restore CA1066
 
     /// <summary>
     /// Smoothing parameter (lambda). Common values: 1600 (Quarterly), 14400 (Monthly), 6.25 (Annual).

lib/filters/hpf/Hpf.cs

@@ -22,8 +22,7 @@ public sealed class Hpf : AbstractBase
     private State _pState;
 
     [StructLayout(LayoutKind.Sequential)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct State
+    private record struct State
     {
         public double Hp1;
         public double Hp2;
@@ -32,7 +31,6 @@ public sealed class Hpf : AbstractBase
         public int Samples;
         public bool HasSrc;
     }
-    #pragma warning restore CA1066
 
     public int Length { get; }
 

lib/filters/kalman/Kalman.cs

@@ -42,14 +42,12 @@ public sealed class Kalman : AbstractBase
     private State _pState;
 
     [StructLayout(LayoutKind.Sequential)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct State
+    private record struct State
     {
         public double X;
         public double P;
         public int Samples;
     }
-    #pragma warning restore CA1066
 
     /// <summary>
     /// Process noise covariance. Defaults to 0.01.

lib/filters/loess/Loess.cs

@@ -28,14 +28,12 @@ public sealed class Loess : AbstractBase
     private Snapshot _pSnap;
 
     [StructLayout(LayoutKind.Sequential)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct Snapshot
+    private record struct Snapshot
     {
         public double LastOutput;
         public double LastFiniteInput;
         public bool HasFiniteInput;
     }
-    #pragma warning restore CA1066
 
     /// <summary>
     /// Gets the period of the filter.

lib/filters/notch/Notch.cs

@@ -15,13 +15,11 @@ public sealed class Notch : AbstractBase
     private State _p_state;
 
     [StructLayout(LayoutKind.Auto)]
-    #pragma warning disable CA1066 // Implement IEquatable<T> because it overrides Equals
-    private struct State
+    private record struct State
     {
         public double X1, X2, Y1, Y2;
         public double LastValue;
     }
-    #pragma warning restore CA1066
 
     public int NotchFreq { get; }
     public double Bandwidth { get; }

lib/filters/usf/Usf.cs

@@ -123,7 +123,10 @@ public sealed class Usf : AbstractBase
 
             double usf = (_state.Count < 4)
                 ? val
-                : (1.0 - _c1) * val + (2.0 * _c1 - _c2) * _state.PrevInput1 - (_c1 + _c3) * _state.PrevInput2 + _c2 * _state.Usf1 + _c3 * _state.Usf2;
+                : Math.FusedMultiplyAdd(_c3, _state.Usf2,
+                    Math.FusedMultiplyAdd(_c2, _state.Usf1,
+                        Math.FusedMultiplyAdd(_k2, _state.PrevInput2,
+                            Math.FusedMultiplyAdd(_k1, _state.PrevInput1, _k0 * val))));
 
             _state.Usf2 = _state.Usf1;
             _state.Usf1 = usf;