More aggressive growth curve in HdyColumn?

HdyColumn was designed primarily for the GNOME Listbox pattern, which is not very information-dense. This is why we chose a non-linear growth curve for the padding, which feels a lot more natural than simple linear growth with a maximum width.

However, we have since found other use cases where this non-linear curve doesn't make sense, because the padding gets in the way of the content at smaller sizes. For example, Fractal's message view currently looks weird with HdyColumn, because of the large padding:

We could solve this problem by optionally offering a more aggressive growth curve, or simply linear growth. Whether this should be a separate widget or an option in HdyColumn I'm not sure, but either way we should communicate clearly where this should be used, so people don't start using it for regular listboxes and we get different apps with inconsistent behaviors.