fix(hosting): use OfType<Type>() in FindXamlMetadataProviderInAssembly

Addresses #144 review feedback. `ex.Types` is `Type?[]`, so the previous
`.Where(t => t is not null).ToArray()!` pattern relied on a nullable
suppression and left a redundant `t is null` check inside the scan loop.
`OfType<Type>().ToArray()` produces a true `Type[]`, eliminating both.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: codemonkeychris

src/Reactor/Hosting/ReactorApp.cs

@@ -111,11 +111,10 @@ public static void RegisterControlAssembly(global::System.Reflection.Assembly as
     {
         global::System.Type[] types;
         try { types = assembly.GetTypes(); }
-        catch (global::System.Reflection.ReflectionTypeLoadException ex) { types = ex.Types.Where(t => t is not null).ToArray()!; }
+        catch (global::System.Reflection.ReflectionTypeLoadException ex) { types = ex.Types.OfType<global::System.Type>().ToArray(); }
 
         foreach (var t in types)
         {
-            if (t is null) continue;
             if (!typeof(IXamlMetadataProvider).IsAssignableFrom(t)) continue;
             if (t.IsAbstract || t.IsInterface) continue;
             if (t.GetConstructor(global::System.Type.EmptyTypes) is null) continue;