Refactor crypto-related traits implementations in term of Public/Signature Bytes (#3806)

Another simple refactory to prune some duplicate code

Follow up of: https://github.com/paritytech/polkadot-sdk/pull/3684

substrate/primitives/statement-store/src/ecies.rs

@@ -148,7 +148,7 @@ mod test {
 	#[test]
 	fn basic_ed25519_encryption() {
 		let (pair, _) = sp_core::ed25519::Pair::generate();
-		let pk = pair.into();
+		let pk = pair.public();
 
 		let plain_message = b"An important secret message";
 		let encrypted = encrypt_ed25519(&pk, plain_message).unwrap();