add PaywallService registration to ServiceCollectionExtensions

[enespaywall]

This pull request introduces a new overloaded method AddPaywallService in the ServiceCollectionExtensions class to provide additional flexibility when configuring paywall-related services.

Key change:

• src/PayWall.NetCore/ServiceCollectionExtensions.cs: Added an overloaded AddPaywallService method that accepts PayWallOptions and an array of DelegatingHandler factories. This method configures multiple API clients (PaymentApiClient, PaymentPrivateApiClient, CardWallApiClient, and MemberApiClient) and registers the PayWallService as a transient service.

[Copilot]

Pull Request Overview

This PR adds an overloaded AddPaywallService extension that accepts a PayWallOptions instance and handler factory delegates for more flexible client configuration.

• Introduced a new AddPaywallService(this IServiceCollection, PayWallOptions, params Func<IServiceProvider, DelegatingHandler>[]) overload
• Registers four API clients and the PayWallService using the provided options and handlers

Comments suppressed due to low confidence (1)

src/PayWall.NetCore/ServiceCollectionExtensions.cs:58

• No unit tests cover this new overload. Add integration or unit tests to verify that all API clients and the PayWallService are registered correctly when using the PayWallOptions overload.

public static void AddPaywallService(