Proper way to construct a WrappedScalar

[apyrgio]

The secp256k1::WrappedScalar has the following constructors:

From<k256::arithmetic::scalar::Scalar>>
From<u64>>

The problems with these constructors are:

• The first constructor requires a Scalar type, which must match the exact same k256 version that vsss_rs uses (currently 0.11, but 0.12 is out). Else, we have this problem:

  error[E0277]: the trait bound `vsss_rs::secp256k1::WrappedScalar: From<Scalar>` is not satisfied
  ...
    = help: the following other types implement trait `From<T>`:
              <vsss_rs::secp256k1::WrappedScalar as From<k256::arithmetic::scalar::Scalar>>
              <vsss_rs::secp256k1::WrappedScalar as From<u64>>
    = note: required for `Scalar` to implement `Into<vsss_rs::secp256k1::WrappedScalar>`
  

• The second constructor will not work with 256-bit keys, if I understand correctly.

There also some other constructors (e.g., from_be_bytes_reduced), but it's not clear how one can use them (not a fault of this repo, the elliptic_curves is a bit lacking in this regard).

Why is the above a problem? Consider someone running the examples in this repo:

use k256::{NonZeroScalar, SecretKey};
[...]

let sk = SecretKey::random(&mut osrng);
let secret = WrappedScalar(*sk.to_nonzero_scalar());

Rust will complain that the Scalar type that vsss_rs expects (0.11) is different from the provided k256::Scalar type (0.12). The only way I've found to circumvent this limitation is to use an older version of k256 (0.11), specifically for importing a k256::SecretKey, which will produce a proper k256::Scalar type (0.11).

This is of course a bit esoteric, and prone to breakage. A better suggestion would be to re-export k256::SecretKey from this module (as k256 already does for the elliptic_curves::SecretKey), and let library consumers use that.

Do you agree, do you perhaps have a better suggestion?