Make LinkAnnotation internal to fix unit tests

src/UglyToad.PdfPig/Writer/LinkAnnotation.cs

@@ -9,7 +9,7 @@ namespace UglyToad.PdfPig.Writer
     /// Represents a link annotation that can be added to a PDF page.
     /// Link annotations provide clickable areas that can trigger actions such as navigating to another page or opening a URL.
     /// </summary>
-    public class LinkAnnotation
+    internal sealed class LinkAnnotation
     {
         /// <summary>
         /// Gets the border style for the link annotation.

src/UglyToad.PdfPig/Writer/PdfPageBuilder.cs

@@ -855,7 +855,7 @@
         /// </summary>
         /// <param name="link">The link annotation to add</param>
         /// <returns>This page builder for method chaining</returns>
-        public PdfPageBuilder AddLink(LinkAnnotation link)
+        private PdfPageBuilder AddLink(LinkAnnotation link)
         {
             links.Add((link.ToToken(), link.Action));
             return this;