Automatically ignore lines containing just an ellipsis

It is common practice, when defining a `typing.Protocol`, to put in an ellipsis as a method stub:

```python
class Proto(typing.Protocol):
    def func(self) -> int:
        ...
```

Since the stubs are never actually called, I have to manually put `# pragma: no cover` after each ellipsis.

Would it make sense for coverage to automatically not cover a line that is just an ellipsis?