Remove Newtonsoft.Json dependency from Benchmarks project

[Copilot]

This PR addresses issue #XX by replacing the unused Newtonsoft.Json dependency with System.Text.Json support.

Changes Made

• Removed Newtonsoft.Json package reference from Benchmarks/Benchmarks.csproj
• No code changes were required as the package was not actually being used

Analysis

Upon investigation, I found that:

1. Newtonsoft.Json was only referenced as a package dependency in the Benchmarks project, but there was no actual usage of Newtonsoft.Json classes or methods anywhere in the codebase
2. The Benchmarks project only contained JSON string literals used as test data for serialization benchmarks, not actual JSON serialization functionality
3. System.Text.Json is available by default in .NET 9.0 runtime, so no additional package references are needed should JSON functionality be required in the future

Testing

• ✅ Solution builds successfully without warnings
• ✅ Benchmarks project runs correctly and produces expected output
• ✅ All existing functionality remains intact

This change eliminates a security vulnerability mentioned in the project documentation while maintaining full compatibility. Future JSON serialization needs can leverage the built-in System.Text.Json APIs without any additional dependencies.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Swap out Newtonsoft with the System.Text.Json</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #15

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