refactor(BurnPdfCommand): extract GdPicture and math helpers into extension classes and simplify BurnPdfCommandHandler

- Refactored BurnPdfCommandHandler to use new extension methods for cleaner annotation handling.
- Introduced ITextStyle interface to generalize font styling for text annotations.
- Updated PDFBurnerParams to implement ITextStyle for consistent font settings reuse.
- Added MathematExtensions for coordinate and unit conversion (ToInches, ToPointF).
- Added GdPictureExtensions to encapsulate annotation-related logic (form fields, images, ink).
- Improved readability and maintainability by removing redundant helper methods.

EnvelopeGenerator.Application/Common/Interfaces/Model/ITextStyle.cs

@@ -0,0 +1,27 @@
+using System.Diagnostics.CodeAnalysis;
+using System.Drawing;
+
+namespace EnvelopeGenerator.Application.Common.Interfaces.Model;
+
+/// <summary>
+/// 
+/// </summary>
+public interface ITextStyle
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    public string FontName { get; set; }
+
+
+    /// <summary>
+    /// 
+    /// </summary>
+    public int FontSize { get; set; }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    [SuppressMessage("Interoperability", "CA1416:Validate platform compatibility", Justification = "<Pending>")]
+    public FontStyle FontStyle { get; set; }
+}