Requiring parameters to be AbstractVectors

[lindnemi]

I think here you are implicitly requiring u0 and p to be AbstractVectors. Hence you might aswell dispatch on that. E.g. this uses tuple parameters and throws an error:

expectation(x -> 1, 
            ODEProblem((a,b,c,d) -> nothing, [1.], (0., 1.), nothing),
            [1.,1.],
            (Uniform(-1,1), 0.), # tuple params
            Koopman(),
            Tsit5())

[ChrisRackauckas]

I see. Yes, that would be good to change.