Migrate from Newtonsoft to System.Text.Json

[EmaX093]

WARNING: Needs thorough testing. It works perfectly on my end, but we should look out for potential edge cases

This pull request migrates the codebase from using Newtonsoft.Json to the built-in System.Text.Json for JSON serialization and deserialization throughout the project. It updates serializer settings, replaces all usages of JsonConvert and related types with their System.Text.Json equivalents, and adjusts code to accommodate API differences. This change reduces external dependencies and leverages the improved performance and features of System.Text.Json.

Migration from Newtonsoft.Json to System.Text.Json:

• All references to Newtonsoft.Json and JsonConvert have been replaced with System.Text.Json and JsonSerializer, including serializer settings and attributes such as [JsonProperty] to [JsonPropertyName].
• The Newtonsoft.Json package reference was removed from the project.
• Serializer options and settings updates
• Code and API adjustments
• Utility classes and extension methods have been updated to use the new serialization APIs and settings.

This migration streamlines JSON handling in the project, aligns with modern .NET practices, and removes a third-party dependency.

[kjeske]

Thank you for the PR!

I see the biggest challange was the JsonPopulate. I think replacing well tested version from Newtonsoft would require writing comprehensive unit tests - without it we cannot be sure the new version works well in all the scenarios.

[EmaX093]

Totally agree! Wrote a json utility to mimic netwonsoft PopulateObject implementation (see JsonPopulator class), but it needs a comprensive set of testing to be sure it doesn't break something.