refactor: unify binding & data provider interfaces

- Removed BindingType enum and all related logic from Binding.
- Made Binding implement new IBinding and IKeyed interfaces.
- Moved node selection logic to IBinding.Select; removed Resolve* methods from Binding.
- Added new IBinding interface for XPath/CssPath selection.
- Refactored IDataProvider to generic IDataProvider<T>; removed GetNode.
- Updated ListContentDataProvider and ParagraphedContentDataProvider to use IBinding.
- Added new ContentsDataProvider, ContentsArrayDataProvider, and DropDownDataProvider for flexible data extraction.
- Updated DataBindings to use IDataProvider<T> properties instead of Binding.
- Updated all usages to new interfaces and patterns.

Beam.Temporary.Cli/CommonTransformers.cs

@@ -11,10 +11,10 @@ namespace Beam.Temporary.Cli {
     public static class CommonTransformers {
         public static AsyncTransformer<HtmlDocument, IDocumentMetaData> ArticleDataTransformer(DataBindings? binding) => (x) => {
             return Task.FromResult<IDocumentMetaData>(new ArticleData() {
-                Authors = [OnlineCleaner.Clean(binding?.Authors?.Resolve(x) ?? "")],
-                Name = OnlineCleaner.Clean(binding?.Title?.ResolveString(x) ?? ""),
-                Categories = OnlineCleaner.Clean(binding?.Tags?.ResolveString(x) ?? "").Split(';') ?? [],
-                Description = OnlineCleaner.Clean(binding?.Description?.ResolveString(x) ?? "")
+                Authors = binding?.Authors?.Get(x)?.Select(OnlineCleaner.Clean)?.ToArray() ?? [],
+                Name = OnlineCleaner.Clean(binding?.Title?.Get(x) ?? ""),
+                Categories = binding?.Tags?.Get(x)?.Select(OnlineCleaner.Clean)?.ToArray() ?? [],
+                Description = OnlineCleaner.Clean(binding?.Description?.Get(x) ?? "")
             });
         };