Breaking Changes in the version4 branch

[CharliePoole]

I'm working on a more complete statement of direction for version 4, but I already have this list of breaking changes, which have already been commited, so I'm posting it separately here.

1. The runner is now called nunit4-console.exe.
2. The DomainUsage and ProjectModel settings and the corresponding console options have been eliminated.
3. Tests may no longer be run in-process. The V3 default model of one process per test assembly is now the only option. Tests are run by agents and the current agents only run a single test assembly per process. NOTE: In a future release, we can provide an in-process agent if there is a need.
4. UserSettings and RecentFiles are no longer tracked by the engine but by the runner. This change impacts third-party developers rather than general users.
5. The API used by extensions has changed so new versions must be created for any extensions to be run under V4.
6. Certain extensions are no longer bundled: TeamCityEventListener, V2 ResultWriter and V2 Frameweork Driver. This is only a packaging change, so could be reversed.
7. The Deprecated --params option has been removed.
8. Some deprecated values of the --labels option have been removed.
9. The --timeout Option is now called --testCaseTimeout.
10. There is now only one constructor for TestPackage, eliminating the problem of divergent semantics between the two constructors supported in version 3.

Work on Version 4 began in 2021, with most work done by Chris Maddock and myself. The first breaking changes were committed in 2022. Initially, v4 work was contained in the main branch, while v3 occupied it's own branch. This was switched in 2024, since most work was continuing on v3. All v4 code is now in a version4 branch. The last commit was in June 2024.

As a general strategy, Chris and I decided to do breaking changes first. Most of the breaking changes involved removal of features and therefore removal of code. This simplified the codebase making it easier to work with as we added new features. Our intent was to restore some capabilities at a later point using an entirely new implementation. One key example of this is in-process execution, which we planned to add back using a custom agent executing in-process.

This strategy was only partially carried out but to the extent we used it we were able to develop new features pretty rapidly. In fact, I continued to use the same approach with the TestCentric engine and GUI and was able to take it a bit further. Some of the features planned for addition to V4 are already present in TestCentric in a more or less compatible implementation.