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.Dynamic/DataBindings.cs

@@ -2,21 +2,21 @@
 
 namespace Beam.Dynamic {
     public record class DataBindings {
-        public Binding? Title { get; set; }
-        public Binding? Authors { get; set; }
-        public Binding? Description { get; set; }
-        public Binding? Content { get; set; }
-        public Binding? Language { get; set; }
-        public Binding? Tags { get; set; }
+        public IDataProvider<string>? Title { get; set; }
+        public IDataProvider<string[]>? Authors { get; set; }
+        public IDataProvider<string>? Description { get; set; }
+        public IDataProvider<string>? Content { get; set; }
+        public IDataProvider<string[]>? Language { get; set; }
+        public IDataProvider<string[]>? Tags { get; set; }
 
         public virtual ResolvedBindings Resolve(HtmlDocument doc) {
             return new ResolvedBindings() {
-                Title = Title?.Resolve(doc),
-                Authors = Authors?.Resolve(doc) ?? Array.Empty<string>(),
-                Language = Language?.Resolve(doc) ?? Array.Empty<string>(),
-                Content = Content?.Resolve(doc),
-                Description = Description?.Resolve(doc),
-                Tags = Tags?.Resolve(doc) ?? Array.Empty<string>()
+                Title = Title?.Get(doc),
+                Authors = Authors?.Get(doc) ?? [],
+                Language = Language?.Get(doc),
+                Content = Content?.Get(doc),
+                Description = Description?.Get(doc),
+                Tags = Tags?.Get(doc) ?? []
             };
         }
     }