Handle Option<&T>

[Gankra]

Option<&T> is an important Rust type for FFI, so we need to support it somehow. Easiest way would be to like, hardcode it as ? and let you write ?&T, maybe only let it work with references..?

Another way would be to define "passthrough types" so you could say like "idk what this is but Rust will know what it is". This kinda sucks though, it would make nullable refs a very verbose idiom. Also idk should ptr and &T be nullable in other languages..?