jacquard-repo: wrong max key length rejects valid keys #40

https://tangled.org/nonbinary.computer/jacquard/blob/8bf1f4146cda70bc7bea9b9527fd1d809dd5d87c/crates/jacquard-repo/src/mst/util.rs#L74-80

    if key.len() > 256 {
        return Err(MstError::KeyTooLong {
            len: key.len(),
            max: 256,
        }
        .into());
    }

the max key length is 830 (317 max collection + / + 512 max rkey)