Move Newtonsoft.Json dependency to separate package

[twogood]

So that we eventually can make a System.Text.Json version as well. See #46

[Copilot]

Pull Request Overview

This PR refactors the JSON serialization dependency by moving Newtonsoft.Json specific implementations into a dedicated package, laying the groundwork for a future System.Text.Json version.

• Renames namespaces from Activout.RestClient.Serialization.Implementation and Activout.RestClient.Test to dedicated Newtonsoft.Json namespaces.
• Updates project files and test suites to reference the new package and calls to the Newtonsoft-specific deserializer and extension method.
• Introduces a new csproj for the separated package and updates dependency and project references accordingly.

Reviewed Changes

Copilot reviewed 39 out of 39 changed files in this pull request and generated 2 comments.

File	Description
Activout.RestClient.Newtonsoft.Json/JsonHelper.cs	Changes namespace to reflect the new package structure.
Activout.RestClient.Newtonsoft.Json/Activout.RestClient.Newtonsoft.Json.csproj	Introduces a new project file with the explicit Newtonsoft.Json dependency.
Activout.RestClient.Newtonsoft.Json.Test/*	Updates test namespaces and client builder invocations to use the new Newtonsoft.Json specific API.

Comments suppressed due to low confidence (1)

Activout.RestClient.Newtonsoft.Json/JsonHelper.cs:3

• The namespace update reflects the new package structure; ensure all internal references and documentation are updated for full consistency.

namespace Activout.RestClient.Newtonsoft.Json

[Copilot]

[nitpick] Consider centralizing dependency version management if applicable, to ensure consistency across the project.