speed up test teardown by now waiting for threads to finish ...

and remove a debug statement

src/key.rs

@@ -90,7 +90,6 @@ impl Key {
     }
 
     pub fn from_slice(bytes: &[u8], key_type: KeyType) -> Option<Self> {
-        println!("hello from_slice");
         let res: Result<Key, _> = match key_type {
             KeyType::Public => SignedPublicKey::from_bytes(Cursor::new(bytes)).map(Into::into),
             KeyType::Private => SignedSecretKey::from_bytes(Cursor::new(bytes)).map(Into::into),