[Milky] Refactor AddApiHandlers method to improve internal structure and maintainability

Author: Linwenxuan04

Lagrange.Milky.Implementation.Api.Generator/MilkyApiHandlerGenerator.cs

@@ -124,11 +124,9 @@ namespace Lagrange.Milky.Extension;
 
         public static partial class ServiceCollectionExtension
         {
-            public static partial TServiceCollection AddApiHandlers<TServiceCollection>(this TServiceCollection services, bool debug) where TServiceCollection : global::Microsoft.Extensions.DependencyInjection.IServiceCollection
+            static partial void AddApiHandlersInternal<TServiceCollection>(TServiceCollection services, bool debug) where TServiceCollection : global::Microsoft.Extensions.DependencyInjection.IServiceCollection
             {
         {{string.Join("\n", infos.Select(info => $"        {(info.Debug ? "if (debug) " : "")}global::Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddKeyedSingleton<global::Lagrange.Milky.Api.Handler.IApiHandler, {info.HandlerTypeFullName}>(services, \"{info.ApiName}\");"))}}
-
-                return services;
             }
         }
         """);

Lagrange.Milky/Extension/ServiceCollectionExtension.cs

@@ -4,5 +4,11 @@ namespace Lagrange.Milky.Extension;
 
 public static partial class ServiceCollectionExtension
 {
-    public static partial TServiceCollection AddApiHandlers<TServiceCollection>(this TServiceCollection services, bool debug) where TServiceCollection : IServiceCollection;
+    public static TServiceCollection AddApiHandlers<TServiceCollection>(this TServiceCollection services, bool debug) where TServiceCollection : IServiceCollection
+    {
+        AddApiHandlersInternal(services, debug);
+        return services;
+    }
+
+    static partial void AddApiHandlersInternal<TServiceCollection>(TServiceCollection services, bool debug) where TServiceCollection : IServiceCollection;
 }