Add support for service key registration

[mokarchi]

Overview

This PR adds support for keyed service registration in the Scan method, enabling compatibility with .NET 8's keyed dependency injection feature. This allows users to specify service keys during scanning, aligning with the AddKeyedSingleton/AddKeyedScoped/AddKeyedTransient pattern introduced in .NET 8.

Problem

Previously, there was no way to register services with keys when using Scrutor's scanning capabilities. Users who wanted to leverage .NET 8's keyed DI feature had to manually register services, losing the benefits of convention-based scanning.

Solution

Added two new methods to ILifetimeSelector:

• WithServiceKey(object serviceKey) - Registers all scanned services with a fixed service key
• WithServiceKey(Func<Type, object?> selector) - Registers services with dynamic keys based on a selector function

Usage Examples

Fixed Service Key

Register all scanned services with the same key:

services.Scan(scan => scan
    .FromAssemblyOf<MyService>()
    .AddClasses()
    .AsImplementedInterfaces()
    .WithServiceKey("my-key")
    .WithTransientLifetime());

// Resolve using the key
var service = provider.GetRequiredKeyedService<IMyService>("my-key");

Dynamic Service Key

Use a selector function to assign different keys based on the implementation type:

services.Scan(scan => scan
    .FromAssemblyOf<IRepository>()
    .AddClasses(c => c.AssignableTo<IRepository>())
    .AsImplementedInterfaces()
    .WithServiceKey(type => type.Name.Replace("Repository", ""))
    .WithScopedLifetime());

// Resolve specific repositories by key
var customerRepo = provider.GetRequiredKeyedService<IRepository>("Customer");
var orderRepo = provider.GetRequiredKeyedService<IRepository>("Order");

[mokarchi]

@khellang Could you review this, please?