Implement SLH-DSA

[paulmillr]

SLH-DSA aka SPHINCS+ is hash-based signature system.

While we still don't know which lattice-based systems would be relevant, SLH seems like a proper idea for many alternative cases. It's also built using old algorithms you already have. Should be simple.

Since your library is the fastest, i'm really curious how fast can SLH-DSA actually be!

https://github.com/paulmillr/noble-post-quantum/blob/main/src/slh-dsa.ts