Refactor DependencyInjection and RepositoryConfiguration classes

Restructure code for improved readability and maintainability. Move RepositoryConfiguration as a nested public class inside DependencyInjection, group related service registration logic, and clarify method organization. No functional changes.

DigitalData.Core.Infrastructure/DependencyInjection.cs

@@ -11,12 +11,7 @@ using System.Linq;
 #endif
 
 namespace DigitalData.Core.Infrastructure
-#if NET
-    ;
-#elif NETFRAMEWORK
 {
-#endif
-
     public static class DependencyInjection
     {
         public static IServiceCollection AddDbRepository(this IServiceCollection services, Action<RepositoryConfiguration> options)
@@ -146,7 +141,4 @@ public static class DependencyInjection
             return services;
         }
     }
-
-#if NETFRAMEWORK
 }
-#endif