[Constructors] Propose type-stable constructors

[lrnv]

The constructors that we have right now are "friendly" in the sense that the dimension d is passed as a parameter to the copulas:

MyCopula(d, args....; kwargs...)

But, sadly, since the dimension $d$ is then used as a type parameter, these constructors are not type stable.

Without removing them, it would be nice to provide type stable ones as

MyCopula{d}(args...; kwargs...)

for every model we have. Unfortunately, for Archimedeans, ExtremeValues and Archimax's, this get a bit more complicated with generators and tails... A question on discourse on this subject: https://discourse.julialang.org/t/write-a-constructor-for-these-aliases/133135/7

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On the other hand, our constructors are not garentied to return the right type since some of them specialize to IndependentCopula, MCopula or WCopula on certain parameters values. This is a behavior that we might want to remove, to encure full stability (and also simplify our fitting procedures).