Fix recursivecopy! for mixed nested VectorOfArray

[JoshuaLampert]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

For VectorOfArrays there was an aliasing issue for mixed nested VectorOfArray. This MWE

using RecursiveArrayTools
using OrdinaryDiffEqSSPRK

function rhs!(du, u, p, t)
    du .= u
    return nothing
end

n = 2
left = ones(n)
right = left

u_flat = VectorOfArray([copy(left), copy(right)])
u_nested = VectorOfArray([copy(left),
                          VectorOfArray([right[e] for e in 1:n])])

tspan = (0.0, 1.0)
prob_flat = ODEProblem(rhs!, u_flat, tspan)
prob_nested = ODEProblem(rhs!, u_nested, tspan)

solver = SSPRK53()
kwargs = (; dt = 0.1, adaptive = false, save_everystep = false)

sol_flat = solve(prob_flat, solver; kwargs...)
sol_nested = solve(prob_nested, solver; kwargs...)

previously returned

julia> sol_nested.u[end]
VectorOfArray{Float64,2}:
2-element Vector{Union{VectorOfArray{Float64, 1, Vector{Float64}}, Vector{Float64}}}:
 [3.6438404308186327, 3.6438404308186327]
 VectorOfArray{Float64, 1, Vector{Float64}}([2.7182551719053256, 2.7182551719053256])

while with this fix this is correct:

julia> sol_nested.u[end]
VectorOfArray{Float64,2}:
2-element Vector{Union{VectorOfArray{Float64, 1, Vector{Float64}}, Vector{Float64}}}:
 [2.7182551719053256, 2.7182551719053256]
 VectorOfArray{Float64, 1, Vector{Float64}}([2.7182551719053256, 2.7182551719053256])

For transparency, I used AI tools to help me come up with this solution.