interfaces: make `dirstate` Protocol class methods abstract Now all known Protocol methods that should be implemented by the subclass are abstract. See cdd4bc69bfc1 for details. Note that this will break the `git` extension more, because there are a bunch of methods that aren't implemented that should be, in favor of some very old methods that won't be called (like `add()` and `drop()`). It's already broken, so I'm not taking the time to figure out how to modernize it right now. It's not detected by pytype because the only instantiation of `gitdirstate` is in `git/__init__.py`, which was already excluded from pytype checking for some other reason. AT least with this, it 1) doesn't get forgotten about, and 2) will require changing the interface if/when the core dirstate class evolves.