Upgrade to .NET 10

[OliverRC]

Upgrade to .NET 10

[OliverRC]

Completed by Sandcastle. Upgraded kickflip and its test project from .NET 8 to .NET 10 (TargetFramework net10.0, LangVersion 14), added actions/setup-dotnet@v4 with dotnet-version 10.0.x to the build and release workflows, and updated the release version-verification path. All 51 tests pass under the .NET 10.0.301 SDK. See PR #17.