New Mapster pre-release packages with .NET 8 and .NET 9 support

[andrerav]

Hi all,

Thank you very much for the patience this last year. I've finally merged most of the waiting PR's and pushed new pre-release packages to NuGet (including Mapster.Tool). Please give it a spin and let me know how it goes. If there are no serious issues I will try to push a full release in a few weeks.