feat: Implement ServiceFactory for dependency injection

- Added ServiceFactory class to manage service registrations and service provider creation.
- Implemented a lazy-loaded IServiceProvider to ensure services are only built once.
- Prevent further modifications to the service collection after the service provider is created.
- Added Provide<T>() method to resolve and retrieve services from the service provider.

DigitalData.Core.Client/BaseHttpClientService.cs

@@ -44,7 +44,10 @@ namespace DigitalData.Core.Client
             if (sendWithCookie)
             {
                 var cookieHeader = _cookies.GetCookieHeader(requestUri);
-                requestMessage.Headers.Add("Cookie", cookieHeader);
+                if (!string.IsNullOrWhiteSpace(cookieHeader))
+                {
+                    requestMessage.Headers.Add("Cookie", cookieHeader);
+                }
             }
 
             // Add body content if provided

DigitalData.Core.Client/DigitalData.Core.Client.csproj

@@ -18,6 +18,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="7.0.0" />
     <PackageReference Include="Microsoft.Extensions.Options" Version="7.0.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
   </ItemGroup>

DigitalData.Core.Client/ServiceFactory.cs

@@ -0,0 +1,21 @@
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DigitalData.Core.Client
+{
+    public static class ServiceFactory
+    {
+        private static readonly IServiceCollection _services = new ServiceCollection();
+        private static readonly Lazy<IServiceProvider> _lazyProvider = new(Build);
+
+        public static IServiceCollection Services => !_lazyProvider.IsValueCreated
+            ? _services
+            : throw new InvalidOperationException(
+                "Service provider has already been created. " +
+                "Further modifications to the service collection are not allowed. " +
+                "This is to ensure that the dependency injection container remains in a consistent state.");
+
+        public static IServiceProvider Build() => _services.BuildServiceProvider();
+
+        public static T Provide<T>() where T : notnull => _lazyProvider.Value.GetRequiredService<T>();
+    }
+}