Possible issue with subclassing SaveOperations that have `needs`

Nobody has claimed this yet.

Working on another PR, so this will need to be investigated. It seems like if you have an SaveOperation that has `needs`, and you subclass that, it will duplicate the instance variable in the constructor causing a compile-time `Error: duplicated argument name: ...` error...

```crystal
class SavePost < Post::SaveOperation
needs rollback : Bool = false

# ...
end

class SubSavePost < SavePost

end

# Error: duplicated argument name: rollback
```

Start by reproducing the shown Crystal example with a SaveOperation that declares needs and a subclass of it. Trace how the needs declaration is turned into constructor arguments and verify the subclass no longer produces the duplicated rollback argument while preserving inherited behavior.

Written by the indexing model from the issue text.