perf(compile_rhs): only calculate tensors that are used in F

[martinjrobins]

at the moment all state dependent tensors are calculated, even those that are used by out but not by F

[martinjrobins]

might be good to build up a tree of tensor dependencies for this, would also help with implementing barriers and reverse-mode autodiff for cranelift

[martinjrobins]

or a simpler thing would just be only calculate tensors written before F