Add support to generate code for interface without a namespace (#46)

src/ProxyInterfaceSourceGenerator/FileGenerators/ProxyClassesGenerator.cs

@@ -84,6 +84,8 @@ internal partial class ProxyClassesGenerator : BaseGenerator, IFilesGenerator
             configurationForMapster = GenerateMapperConfigurationForMapster();
         }
 
+        var (namespaceStart, namespaceEnd) = NamespaceBuilder.Build(pd.Namespace);
+
         return $@"//----------------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by https://github.com/StefH/ProxyInterfaceSourceGenerator.
@@ -96,8 +98,7 @@ internal partial class ProxyClassesGenerator : BaseGenerator, IFilesGenerator
 {(SupportsNullable ? "#nullable enable" : string.Empty)}
 using System;
 
-namespace {pd.Namespace}
-{{
+{namespaceStart}
     public {@abstract}partial class {className} : {extends}{interfaceName}
     {{
         public {@new}{targetClassSymbol.Symbol} _Instance {{ get; }}
@@ -117,7 +118,7 @@ namespace {pd.Namespace}
 {configurationForMapster}
         }}
     }}
-}}
+{namespaceEnd}
 {(SupportsNullable ? "#nullable disable" : string.Empty)}";
     }