Add static BuildStaticClient method with Obsolete warning

A new static method `BuildStaticClient(Action<HttpClient> configureClient)`
was added to the `ReC.Client` namespace in `ReCClient.cs`. This method
configures and builds a static `IServiceProvider` for creating `ReCClient`
instances. It includes XML documentation detailing its purpose, usage,
and parameters, and warns that it should only be called once during
application startup.

The method accepts an `Action<HttpClient>` parameter for `HttpClient`
configuration and throws an `InvalidOperationException` if the static
provider is already built. It is marked `[Obsolete]` to encourage the
use of a local service collection instead of the static provider.

Additionally, the XML documentation for the `ReCClient` creation method
was updated to reference the new `BuildStaticClient` method.

src/ReC.Client/ReCClient.cs

@@ -88,6 +88,24 @@ namespace ReC.Client
             Provider = Services.BuildServiceProvider();
         }
 
+        /// <summary>
+        /// Configures and builds the static <see cref="IServiceProvider"/> for creating <see cref="ReCClient"/> instances.
+        /// </summary>
+        /// <remarks>
+        /// This method should only be called once during application startup.
+        /// </remarks>
+        /// <param name="configureClient">An action to configure the <see cref="HttpClient"/>.</param>
+        /// <exception cref="InvalidOperationException">Thrown if the static provider has already been built.</exception>
+        [Obsolete("Use a local service collection instead of the static provider.")]
+        public static void BuildStaticClient(Action<HttpClient> configureClient)
+        {
+            if (Provider != null)
+                throw new InvalidOperationException("Static Provider is already built.");
+
+            Services.AddRecClient(configureClient);
+            Provider = Services.BuildServiceProvider();
+        }
+
         /// <summary>
         /// Creates a new <see cref="ReCClient"/> instance using the statically configured provider.
         /// </summary>