A lot of ambiguities due to too general `rand`signatures

We are still using this quite heavily in Oscar land, but after playing around with https://github.com/JuliaTesting/Aqua.jl (which helps detecting method ambiguities), I noticed that RandomExtensions.jl leads to a lot of method ambiguities. For example, the methods
```
rand(X, ::Type{Tuple}, n::Integer)
@ RandomExtensions ~/.julia/packages/RandomExtensions/qAD6J/src/containers.jl:53
rand(X, t::Type{<:Array}, dims::Integer...)
@ RandomExtensions ~/.julia/packages/RandomExtensions/qAD6J/src/containers.jl:106
```
will make the pass-through methods
```
rand(T::MyAbstractType, v...) = rand(GLOBAL_RNG, T, v...)
```
ambiguous for certain input types (note that I cannot pin down the type of `v` directly, since `T` is abstract and there are many possible combinations).

They are usually fine in practice, but it just looks bad. There are so many, that ignoring them might hide real ambiguities.

Start by reproducing the ambiguity reports with Aqua.jl and inspect the methods shown in src/containers.jl, especially the definitions around lines 53 and 106. Trace how they interact with the pass-through rand(T::MyAbstractType, v...) method; done means the relevant ambiguities are understood and the project has a defined way to address or validate them.

Scritto dal modello di indicizzazione a partire dal testo della issue.