Add Ehlers Hilbert Transform Instantaneous Trend (HTIT) implementation and tests

- Implemented the HTIT indicator in Htit.cs, utilizing the Hilbert Transform for trend analysis.
- Added unit tests for HTIT validation against TA-Lib, Skender, and Ooples implementations in Htit.Validation.Tests.cs.
- Created documentation for HTIT in Htit.md, detailing its core concepts, formula, parameters, usage, and interpretation.

lib/core/tbarseries/tbarseries.cs

@@ -21,12 +21,12 @@ public class TBarSeries : IReadOnlyList<TBar>
     public string Name { get; set; } = "Bar";
     public event Action<TBar>? Pub;
 
+    // Note: These views share underlying storage. Do not modify directly; use TBarSeries.Add() instead.
     public TSeries Open { get; }
     public TSeries High { get; }
     public TSeries Low { get; }
     public TSeries Close { get; }
     public TSeries Volume { get; }
-
     // Aliases for convenience
     public TSeries O => Open;
     public TSeries H => High;