feat: derive Clone for KeyPair and XKey

Allow KeyPair and XKey structs to be cloned. We have no technical reason
not to do this, since it is trivial to copy out a private key from
either key type and the underlying members of the struct are all already
Clone.

Signed-off-by: Dan Norris <[email protected]>

src/lib.rs

@@ -87,7 +87,8 @@ const PUBLIC_KEY_PREFIXES: [u8; 8] = [
 type Result<T> = std::result::Result<T, crate::error::Error>;
 
 /// The main interface used for reading and writing _nkey-encoded_ key pairs, including
-/// seeds and public keys. Instances of this type cannot be cloned.
+/// seeds and public keys.
+#[derive(Clone)]
 pub struct KeyPair {
     kp_type: KeyPairType,
     sk: Option<SecretKey>, //rawkey_kind: RawKeyKind,

src/xkeys.rs

@@ -17,7 +17,8 @@ use crypto_box::{PublicKey, SecretKey};
 use rand::{CryptoRng, Rng, RngCore};
 
 /// The main interface used for reading and writing _nkey-encoded_ curve key
-/// pairs. Instances of this type cannot be cloned.
+/// pairs.
+#[derive(Clone)]
 pub struct XKey {
     public: PublicKey,
     secret: Option<SecretKey>,