Make inline-block layout type-safe :)

[afishhh]

I had some fun.

We love zero-cost abstractions over here. This is just like C++ :)

[afishhh]

Not sure whether this is worth the complexity right now but this proves it is possible to get rid of those nasty assertions in a zero-cost fashion.
In reality it'd probably suffice to just use a normal generic and live with the realloc(s) when entering layout but that's not any fun.
(though I haven't even tested if this avoids the realloc lol)