Update Rive.Maui NuGet Package for .NET 9 Support

[danielmonettelli]

Hello @matmork and @hansmbakker , first of all, thank you for creating such a fantastic NuGet package that allows using Rive with .NET MAUI. I was wondering if it would be possible to update the package to support .NET 9. Thank you very much in advance for your attention!

[matmork]

Hi! I am working on a .NET 9 branch here #30 :)

Still needs some work updating Rive versions etc. but you can test it out if you want to. Download NuGet from https://github.com/matmork/rive-maui/actions/runs/12117397310

[danielmonettelli]

Thank you very much, I will give it a try. I truly appreciate that you are accelerating the development of Rive with .NET MAUI for .NET 9.