math.randomseed with two arguments fails on 32-bit targets (wasm32)

[evrimoztamur]

In src/stdlib/math.rs:340, the seed array is hardcoded as [u8; 32]:

let seed: [u8; 32] = core::array::from_fn(|idx| { ... });

On 32-bit targets (e.g. wasm32-unknown-unknown), SmallRng is Xoshiro128PlusPlus
with a 16-byte seed, so SmallRng::from_seed(seed) fails to compile:

expected an array with a size of 16, found one with a size of 32

Fix: replace the hardcoded size with the associated type:

let seed: <SmallRng as SeedableRng>::Seed = core::array::from_fn(|idx| { ... });