Relocate JSON features to its own utility library

[AlexNachbaur]

This follows on #257, separating JSON features into a stand-alone library. This is to lay the groundwork to simplify the changes in #248.

[Copilot]

Pull Request Overview

This PR relocates JSON functionality into a separate utility library, following PR #257 and preparing for the changes in PR #248. This refactoring improves modularity by extracting JSON-related features from the main AuthFoundation library.

• Creates a new standalone JSON library module
• Updates import statements across the codebase to use the new JSON library
• Modifies package configuration and podspec to include the new JSON target

Reviewed Changes

Copilot reviewed 22 out of 23 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Package.swift	Adds new JSON library target and updates dependencies
OktaAuthFoundation.podspec	Includes JSON source files in the podspec
Sources/AuthFoundation/*	Updates files to import the new JSON module
Sources/OktaIdxAuth/*	Updates files to import the new JSON module
Sources/OktaDirectAuth/*	Updates files to import the new JSON module
Tests/JSONTests/*	Adds new test files for the JSON module
Tests/*/Tests.swift	Updates test files to import the new JSON module

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[IldarAbdullin-okta]

LGTM!

The base branch was changed.