Adopt .NET 10

Adopt .NET 10.

We will also support .NET 8 and utilize multitargeting.

The tests and all other components will use .NET 10 after this change.

Upgrade also to the latest NuGet packages, including https://github.com/spectreconsole/spectre.console.
Be aware that there were some issues with upgrading the Spectre console in the past; there is probably a bug or a breaking change.