Function xmss_sign 

pub fn xmss_sign<P: Params>(
    m: &[u8],
    sk_seed: &[u8],
    idx: u32,
    pk_seed: &[u8],
    adrs: &mut Adrs,
) -> Vec<u8> 

Create an XMSS signature for an n-byte message.

Implements Algorithm 10 of FIPS 205. Signs message m using the WOTS+ key pair at leaf index idx and produces an authentication path of h' sibling nodes that allows the verifier to recompute the tree root.

The returned signature is (len + h') * n bytes: a WOTS+ signature (len * n) followed by the Merkle authentication path (h' * n).