Build using NUnit.Cake.Recipe

[CharliePoole]

The recipe is now used for building main but the version4 branch still has custom cake scripts. We should use the recipe for both, although it's possible to specify a different version of the recipe in each case should the need arise.

[CharliePoole]

Many changes involved here because the recipe expects that all references have been updated. So the PR will include:

• Adding a .NET 8.0 engine
• Updating nunit.framework versions

Some changes regarding extensions are postponed until both the extension manager and the extensions themselves have been updated.

[CharliePoole]

This issue has been resolved in version 4.0.0-beta.1

The release is available on:
GitHub.
NuGet packages are also available NuGet.org and
Chocolatey Packages may be found at Chocolatey.org