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.