Validation work

Toolkit.Foundation/IValidatorCollection.cs

@@ -0,0 +1,11 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace Toolkit.Foundation;
+
+public interface IValidatorCollection :
+    IReadOnlyCollection<Validator>
+{
+    void Add(string key, Validator binder);
+
+    bool TryGet(string key, [MaybeNull] out Validator? value);
+}