* `-Dskip-compile-errors` is removed; `-Dskip-stage1` is added.
* Use `std.testing.allocator` instead of a new instance of GPA.
- Fix the memory leaks this revealed.
* Show the file name when it is not parsed correctly such as when the
manifest is missing.
- Better error messages when test files are not parsed correctly.
* Ignore unknown files such as swap files.
* Move logic from declarative file to the test harness implementation.
* Move stage1 tests to stage2 tests where appropriate.