Function ht_verify 

pub fn ht_verify<P: Params>(
    m: &[u8],
    sig_ht: &[u8],
    pk_seed: &[u8],
    idx_tree: u64,
    idx_leaf: u32,
    pk_root: &[u8],
) -> bool

Verify a hypertree signature.

Implements Algorithm 13 of FIPS 205. Recomputes the XMSS root at each of the d layers, starting from the signed message m at layer 0 and propagating upward. Returns true if the reconstructed top-layer root matches pk_root.

Each XMSS signature in sig_ht is (len + h') * n bytes; the full hypertree signature contains d such signatures.