Support vectorizing `rand`?

I have no idea if it is possible to vectorize `rand`.

I hope for a usage like below:

```julia
julia> using LoopVectorization

julia> m = zeros(Float32, 4,4)
4×4 Matrix{Float32}:
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0

julia> a = rand(Float32, 4,4)
4×4 Matrix{Float32}:
0.251334 0.409923 0.591477 0.04535
0.4116 0.52253 0.34138 0.870923
0.24401 0.116969 0.583924 0.0549548
0.528378 0.898528 0.519574 0.172627

julia> b = rand(Float32, 4,4)
4×4 Matrix{Float32}:
0.874233 0.263186 0.000970364 0.411874
0.0680491 0.951124 0.803958 0.197752
0.669292 0.996646 0.0915098 0.652465
0.395592 0.875268 0.601194 0.518282

julia> @avxt for i in eachindex(m)
m[i] = rand(a[i]:1.0f3:b[i])
end
```

I have tried `VectorizedRNG` but I did not find out how to set boundries.

Start with the @avxt loop and the VectorizedRNG approach mentioned in the issue, then inspect how LoopVectorization handles rand calls and bounds. Clarify the intended per-element boundary behavior for the a and b arrays. Done means the shown loop can generate bounded random values through vectorization, with tests covering the supported usage.

索引モデルが issue の本文から書いたものです。