Improve Robustness to RATv3

[ChrisRackauckas]

Since AbstractVectorOfArray should be handled properly given the deprecation warning

[AayushSabharwal]

So the issue with this is the following (so far as I can determine):
In this line of Zygote, it maps over a VectorOfArray y∂b. The code expects that iterating over it will yield items of type eltype(y∂b), but VoA doesn't work like that and yields the subarrays instead, which breaks the code

EDIT: so fixing this and reusing the Zygote.unbroadcast(::AbstractArray, ...) dispatch for ::AbstractVectorOfArray fixes this issue, but there's another error further in

[AayushSabharwal]

The "fix" I have is also not great. There's the underlying issue that sometimes Zygote turns VectorOfArrays into Refs containing a NamedTuple. There's a hack around this in RAT's ZygoteExt, but it crops up here too.

While stepping through Zygote:

1|julia> ȳ
Base.RefValue{Any}((u = [[1.0, 0.0, 4.0, 0.0], [1.0, 0.0, 4.0, 0.0]],))

This should be a VectorOfArray

[ChrisRackauckas]

Oh that means that the constructor of a VectorOfArray is missing a chain rule.

[AayushSabharwal]

Could it also be that the Array(::VectorOfArray) functions are missing an adjoint? Adding one for that fixed it for me

[ChrisRackauckas]

Ahh that could do it.

[AayushSabharwal]

I think we also need a method for this:

ERROR: MethodError: no method matching (::ChainRulesCore.ProjectTo{VectorOfArray, NamedTuple{(), Tuple{}}})(::Vector{Float64})

[AayushSabharwal]

I don't fully understand what Zygote.unbroadcast is supposed to do. I hacked together something that works specifically for VectorOfArray, but it doesn't work for ODESolution