Allow subscription keys to be resolved by reflection

Toolkit.Foundation/Mediator.cs

@@ -32,7 +32,7 @@ public class Mediator(IHandlerProvider handlerProvider,
             }
         }
 
-        foreach (object? handler in handlerProvider.Get(messageType))
+        foreach (object? handler in handlerProvider.Get(messageType, key))
         {
             if (handler is not null)
             {

Toolkit.Foundation/ObjectExtensions.cs

@@ -9,8 +9,7 @@ public static class ObjectExtensions
         Type type = obj.GetType();
 
         object? key = selector();        
-        if (type.GetProperty($"{key}") is PropertyInfo property
-            && property.GetValue(obj) is { } value)
+        if (type.GetProperty($"{key}") is PropertyInfo property && property.GetValue(obj) is { } value)
         {
             return value;
         }

Toolkit.Foundation/Observable.cs

@@ -120,17 +120,24 @@ public partial class Observable<TValue>(IServiceProvider provider,
     private TValue? value = value;
 }
 
-public partial class Observable<TKey, TValue>(IServiceProvider provider,
-    IServiceFactory factory,
-    IMediator mediator,
-    IPublisher publisher,
-    ISubscription subscriber,
-    IDisposer disposer,
-    TValue? value = default) : Observable(provider, factory, mediator, publisher, subscriber, disposer)
+public partial class Observable<TKey, TValue> : Observable
 {
     [ObservableProperty]
     private TKey? key;
 
     [ObservableProperty]
-    private TValue? value = value;
+    private TValue? value;
+
+    public Observable(IServiceProvider provider, 
+        IServiceFactory factory,
+        IMediator mediator, 
+        IPublisher publisher, 
+        ISubscription subscriber, 
+        IDisposer disposer,
+        TKey? key = default,
+        TValue? value = default) : base(provider, factory, mediator, publisher, subscriber, disposer)
+    {
+        Key = key;
+        Value = value;
+    }
 }

Toolkit.Foundation/Subscription.cs

@@ -120,8 +120,15 @@ public class Subscription(SubscriptionCollection subscriptions,
                 keys[attribute.Type] = value;
             }
 
+            if (subscriber.GetPropertyValue(() => attribute.Key) is object key)
+            {
+                value.Add(key);
+            }
+            else
+            {
                 value.Add(attribute.Key);
             }
+        }
 
         return keys;
     }