Handle warnings and let users use AddOpenApi instead of WithOpenApi

Net.Sdk.Web.Extensions.SourceGenerators/Net.Sdk.Web.Extensions.SourceGenerators.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-    <Version>0.9.3</Version>
+    <Version>0.9.4</Version>
     <LangVersion>latest</LangVersion>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <Authors>Alexandru Macocian</Authors>

Net.Sdk.Web.Extensions.SourceGenerators/UseRoutesGenerator.cs

@@ -193,7 +193,7 @@ public class UseRoutesGenerator : IIncrementalGenerator
             builder.WithUsing(classUsing);
         }
 
-        var fileSource = builder.Build().ToFullString();
+        var fileSource = $"#nullable enable\n{builder.Build().ToFullString()}\n#nullable disable";
         sourceProductionContext.AddSource($"{Constants.EndpointRouteBuilderExtensionsName}.g", fileSource);
     }
 
@@ -259,7 +259,6 @@ public class UseRoutesGenerator : IIncrementalGenerator
         {
             var methodSymbol = semanticModel.GetDeclaredSymbol(methodDeclarationSyntax);
             AddProducesResponseTypeExtension(methodSymbol, extensionsBuilder);
-            extensionsBuilder.AppendLine($"\n.{Constants.WithOpenApiExtension}()");
         }
 
         /*