System.Text.Json support via new Activout.RestClient.Json package

[twogood]

Resolves #46

[Copilot]

Pull Request Overview

This PR adds support for System.Text.Json serialization and deserialization by introducing a new package, Activout.RestClient.Json. Key changes include:

• New serializer and deserializer classes using System.Text.Json with support for custom options.
• A default configuration class along with a JSON converter for simple value objects.
• Extension methods and tests ensuring proper integration and behavior.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
ActivoutRestClient.sln	Added new projects for Activout.RestClient.Json and its tests.
SystemTextJsonSerializer.cs	Implements JSON serialization using System.Text.Json.
SystemTextJsonDeserializer.cs	Implements JSON deserialization using System.Text.Json.
SystemTextJsonDefaults.cs	Provides default serializer options and supported media types.
SimpleValueObjectConverter.cs	Adds a JSON converter for simple value objects.
RestClientBuilderJsonExtensions.cs	Registers the serializer and deserializer via extension method.
README.md	Documents the usage of Activout.RestClient.Json.
Activout.RestClient.Json.csproj	Project configuration for the new JSON package.
SystemTextJsonDeserializerTest.cs	Tests for verifying JSON deserialization behavior.
SimpleValueObjectTest.cs	Tests for verifying serialization and deserialization of value objects.
Activout.RestClient.Json.Test.csproj	Project configuration for the test project.