Replace golang.org/x/exp/rand with math/rand/v2

[Juneezee]

We have upgraded our minimum Go version to 1.23 in PR #1016.

Go 1.22 introduces the new math/rand/v2 package ¹, which is intended to replace golang.org/x/exp/rand as proposed in golang/go#61716.

Once math/rand/v2 has shipped, we would tag and delete x/exp/rand.

Footnotes

1. https://go.dev/doc/go1.22#math_rand_v2 ↩

[sbinet]

we'll need Gonum to update to the new API before Go-HEP can as well.
(we are e.g. using gonum/stat/distuv)

• all: consider using math/rand/v2 when available gonum/gonum#1906