Upgrade rand package to use math/rand or math/rand/v2

[sjsanc]

The rand package uses the math/crypto package from the standard library. The random number generator from crypto is meant to generate secure numbers, and is therefore much slower than math/rand/v2, or even math/rand.

math/rand/v2 was added in 1.22 (we're on 1.23).

It's also a simpler implementation.

// Using math/rand/v2
func numberMathRandV2() (int64, error) {
	return randv2.Int64(), nil
}

[kashifkhan0771]

Great finding @sjsanc ❤️