refactor: modularize Beam into new projects and interfaces

- Introduced modularity by splitting Beam into new projects: Beam.Abstractions, Beam.Models, and Beam.Downloaders.
- Refactored existing classes into appropriate namespaces and projects.
- Replaced specific implementations with abstractions (e.g., SourceLinkBuilder to LinkBuilder, State to IState, etc.).
- Updated interfaces: added ITemplate, IArticleData, IDownloadReport, and others for improved extensibility.
- Removed deprecated classes like SourceLinkBuilder and StateChangerFactory.
- Enhanced link handling in downloaders by refactoring to use `string` over `SourceLink`.
- Consolidated shared logic under Beam.Abstractions.

Beam.Dynamic/AnchorCollectionDataProvider.cs

@@ -6,7 +6,7 @@ using System.Text;
 using System.Threading.Tasks;
 
 namespace Beam.Dynamic {
-    public class AnchorCollectionDataProvider : IDataProvider<string[]>, IDataProvider<SourceLink[]> {
+    public class AnchorCollectionDataProvider : IDataProvider<string[]> {
         public IBinding? Content { get; set; }
         public string? RelativeTo { get; set; }
 
@@ -35,19 +35,5 @@ namespace Beam.Dynamic {
 
             return links.Where(x => !string.IsNullOrWhiteSpace(x)).ToArray();
         }
-
-        SourceLink[] IDataProvider<SourceLink[]>.Get(HtmlDocument document) {
-            var links = Get(document);
-
-            if (links.Length == 0)
-                return [];
-
-            List<SourceLink> slinks = [];
-            foreach (var link in links)
-                if (Uri.TryCreate(GetAbsolute(RelativeTo, link), UriKind.RelativeOrAbsolute, out _))
-                    slinks.Add(new SourceLink(GetAbsolute(RelativeTo, link)));
-
-            return slinks.ToArray();
-        }
     }
 }