Should Signer consume SecretKey on creation?

[fjarri]

This is the case for SigningKey in RustCrypto. But what dangerous scenarios does that really prevent?

For those not familiar with the concept in Rust: currently one can do this:

let sk = SecretKey::random();
let signer = Signer::new(&sk); // passed by reference, cloned inside
// `sk` still usable here

A possible change matching SigningKey behavior is to do this:

let sk = SecretKey::random();
let signer = Signer::new(sk); // passed by value and consumed
// `sk` cannot be used anymore