Using cast from generics requires simba

[NipaJ]

I implemented generic axis-aligned bounding box struct that uses OPoint. I was trying to replicate OPoint::cast for my bounding box struct. This was not possible without adding simba as dependency to my crate and bringing in simba::scalar::SubsetOf trait.

[sebcrozet]

I think we should re-export simba from nalgebra.

[cayv]

Just came here to create an issue about the same problem. I had to add simba as a dependency just because I needed ClosedNeg.