Function slh_verify 

pub fn slh_verify<P: Params>(
    m: &[u8],
    sig: &[u8],
    pk: &[u8],
) -> Result<bool, SlhDsaError>

Verify an SLH-DSA signature against a message and public key.

Implements Algorithm 24 of FIPS 205. Validates the key and signature lengths, then delegates to slh_verify_internal.

Returns Ok(true) if valid, Ok(false) if the signature does not verify, or Err if the key or signature has an invalid length.