Dual value tests broken

[matbesancon]

Multiple tests on dual values are broken, with the following form:

Differentiating a simple PSD: Error During Test at /home/mbesancon/Documents/crptests/project_julia/DiffOpt.jl/test/MOI_wrapper.jl:794
  Test threw exception
  Expression: ≈(y, [0.33333333, -0.23570226, -0.23570226, 0.33333333, -0.23570226, 0.33333333], atol = ATOL, rtol = RTOL)
  DimensionMismatch("dimensions must match: a has dims (Base.OneTo(1),), b has dims (Base.OneTo(6),), mismatch at 1")

y is a Vector{Union{Float64, Vector{Float64}}} and cannot be compared with a simple vector of floats

[matbesancon]

1. the structure of the dual variables should be documented somewhere
2. the tests should be fixed and we should make sure they don't rely on a constraint order that should not be assumed

[matbesancon]

ping @Aks1996

[matbesancon]

I'll close this as corrected by the PR integrating MatOI