fix: adds Generated suffix to generated files namespace to avoid uninteded using

Author: mrdevrobot

Concordia.Generator/ConcordiaGenerator.cs

@@ -194,7 +194,7 @@ private static string GenerateHandlersRegistrationCode(string methodName, string
         sb.AppendLine("using Microsoft.Extensions.DependencyInjection;");
         sb.AppendLine("using Concordia;");
         sb.AppendLine();
-        sb.AppendLine($"namespace {generatedNamespace}");
+        sb.AppendLine($"namespace {generatedNamespace}.Generated");
         sb.AppendLine("{");
         sb.AppendLine($"    public static class ConcordiaGeneratedRegistrations");
         sb.AppendLine("    {");