`GenAlignment` is used to control generation alignment, while `SpaceAlignment` handles space-alignment within a generation. Technically, they can have different values, but in our implementation, they never do.

Currently, `GenAlignment` is only used in Serial and Parallel collectors, and in all cases, we have (effectively):

```
SpaceAlignment = GenAlignment = ...
```

Allowing/supporting different values could introduce unnecessary complexity. Therefore, I suggest removing `GenAlignment` and use `SpaceAlignment` instead.