Issue with OrdinaryDiffEq.jl when using an ArrayPartition of Arrays of StaticArrays

Start by running the supplied MWE with StaticArrays, StructArrays, RecursiveArrayTools, and OrdinaryDiffEq. Inspect src/array_partition.jl around the copyto! implementation at lines 327-329, along with the reported eltype behavior and StructArrays conversion stacktrace. Done means the MWE no longer raises the Float64-to-SVector conversion MethodError.

OrdinaryDiffEq.jl has an issue with ArrayPartitions constructed from nested arrays of StaticArrays. The following MWE

using StaticArrays, StructArrays
using RecursiveArrayTools
using OrdinaryDiffEq

u1 = StructArray{SVector{2, Float64}}(ntuple(x -> x * ones(10), 2))
u2 = deepcopy(u1)
u = ArrayPartition(u1, u2)

function rhs!(du, u, p, t) 
    du .= u
end
prob = ODEProblem(rhs!, u, (0, 1.0))
sol = solve(prob, Tsit5())

yields the stacktrace

ERROR: MethodError: Cannot `convert` an object of type Float64 to an object of type SVector{2, Float64}
Closest candidates are:
  convert(::Type{SA}, ::Tuple) where SA<:StaticArray at ~/.julia/packages/StaticArrays/0T5rI/src/convert.jl:171
  convert(::Type{SA}, ::SA) where SA<:StaticArray at ~/.julia/packages/StaticArrays/0T5rI/src/convert.jl:170
  convert(::Type{SA}, ::StaticArray{S}) where {SA<:StaticArray, S<:Tuple} at ~/.julia/packages/StaticArrays/0T5rI/src/convert.jl:164
  ...
Stacktrace:
  [1] maybe_convert_elt(#unused#::Type{SVector{2, Float64}}, vals::Float64)
    @ StructArrays ~/.julia/packages/StructArrays/rICDm/src/utils.jl:197
  [2] setindex!
    @ ~/.julia/packages/StructArrays/rICDm/src/structarray.jl:363 [inlined]
  [3] macro expansion
    @ ./broadcast.jl:961 [inlined]
  [4] macro expansion
    @ ./simdloop.jl:77 [inlined]
  [5] copyto!
    @ ./broadcast.jl:960 [inlined]
  [6] copyto!
    @ ./broadcast.jl:913 [inlined]
  [7] f
    @ ~/.julia/packages/RecursiveArrayTools/YoTgv/src/array_partition.jl:327 [inlined]
  [8] ntuple
    @ ./ntuple.jl:49 [inlined]
  [9] copyto!
    @ ~/.julia/packages/RecursiveArrayTools/YoTgv/src/array_partition.jl:329 [inlined]
 [10] materialize!
    @ ./broadcast.jl:871 [inlined]
 [11] materialize!
    @ ./broadcast.jl:868 [inlined]
 [12] fast_materialize!
    @ ~/.julia/packages/FastBroadcast/fkwMa/src/FastBroadcast.jl:47 [inlined]
 [13] ode_determine_initdt(u0::ArrayPartition{Float64, Tuple{StructVector{SVector{2, Float64}, Tuple{Vector{Float64}, ....

I'm not sure but this seems to be related to the fact that eltype of ArrayPartitions of AbstractArray{<:StaticArray{N,T}} is T rather than StaticArray{N,T}.