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/Binding.cs

@@ -1,69 +1,19 @@
 
 using aeqw89.DataKeys;
 using HtmlAgilityPack;
+using System.Text.Json;
 using System.Text.Json.Serialization;
 
 namespace Beam.Dynamic {
-    public class Binding(DataKey<Binding> key) : IKeyed<Binding> {
+    public class Binding(DataKey<Binding> key) : IBinding, IKeyed<Binding> {
         public Binding(string key) : this(new DataKey<Binding>(key)) { }
         public Binding() : this("") { }
 
         [JsonRequired]
         public DataKey<Binding> Key { get; set; } = key;
-        [JsonRequired]
-        public BindingType Type { get; set; }
 
-        public string? ArrayDelimiters { get; set; }
         public string? XPath { get; set; }
         public string? CssPath { get; set; }
         public string? Text { get; set; }
-        private IDataProvider? Provider_;
-        public IDataProvider? Provider {
-            get => Provider_;
-            set {
-                if (value is null)
-                    return;
-                if (value is not IDataProvider)
-                    throw new InvalidOperationException();
-                var constructor = value.GetType().GetConstructor([]);
-                if (!constructor?.IsPublic ?? true)
-                    throw new InvalidOperationException();
-                Provider_ = value;
-            }
-        }
-
-        public HtmlNode? ResolveNode(HtmlDocument doc) {
-            if (XPath is not null)
-                return doc.DocumentNode.SelectSingleNode(XPath);
-            if (CssPath is not null)
-                return doc.DocumentNode.ThenByClasses(CssPath.Split('/'));
-            if (Provider is not null)
-                return Provider.GetNode(doc);
-            return null;
-        }
-
-        public string ResolveString(HtmlDocument doc) {
-            if (XPath is not null)
-                return doc.DocumentNode.SelectSingleNode(XPath)?.InnerText ?? "";
-            if (CssPath is not null)
-                return doc.DocumentNode.ThenByClasses(CssPath.Split('/'))?.InnerText ?? "";
-            if (Provider is not null)
-                return Provider.Get(doc);
-            return "";
-        }
-
-        public string[] ResolveArray(HtmlDocument doc) {
-            if (Type is not BindingType.Array)
-                return [];
-            var str = ResolveString(doc);
-            return str.Split(ArrayDelimiters);
-        }
-
-        public dynamic? Resolve(HtmlDocument doc) => Type switch {
-            BindingType.Single => ResolveString(doc),
-            BindingType.Array => ResolveArray(doc),
-            BindingType.UseProvider => Provider?.Get(doc),
-            _ => null
-        };
     }
 }