secrecy: make integer primitive SecretSlices cloneable

[tony-iqlusion]

Impls Clone for SecretSlice when the S generic type is CloneableSecret + Zeroize.

As originally requested in #1070, also marks the integer primitive types as CloneableSecret, which makes it possible to clone a SecretSlice<u8>.

Closes #1233

[nbari]

Hi @tony-iqlusion before this used to work Secret<[u8, 32]> I am trying now SecretSlice<[u8; 32]> but I get:

the trait `Zeroize` is not implemented for `[[u8; 32]]`

my trait function looks like:

// Define a trait for cryptographic algorithms
pub trait Crypto {
    fn new(key: SecretSlice<[u8; 32]>) -> Self;
    fn encrypt(&self, data: &[u8], fingerprint: &[u8]) -> Result<Vec<u8>>;
    fn decrypt(&self, data: &[u8], fingerprint: &[u8]) -> Result<Vec<u8>>;
}

Any ideas on how to make it work of how to migrate from secret 0.8?

[tony-iqlusion]

You'd probably want SecretBox in this case, not SecretSlice, since that would create a slice of arrays.

I think the best fix here might be to impl ClonableSecret for all arrays whose inner T is a ClonableSecret.

[nbari]

Hi @tony-iqlusion I ended up using SecretSlice<u8> seems to be doing the trick, If I understand it is just a vector of unspecified size the one I can later just fill with <[u8, 32>] or am I missing something? Just in case I am using it here:
https://github.com/ssh-vault/ssh-vault/blob/develop/src/vault/crypto/mod.rs#L13

That is allowing me to use .clone() https://github.com/ssh-vault/ssh-vault/blob/develop/src/vault/ssh/ed25519.rs#L62-L63