Handler::register should be use a a password generator that implements Send

[nanu-c]

In order to register in a thread, the all functions should implement the Send trait.

We could change -> https://github.com/whisperfish/presage/blob/main/src/manager.rs#L189

        // generate a random 24 bytes password
        let rng = rand::thread_rng();
        let password: String = rng.sample_iter(&Alphanumeric).take(24).collect();

to

        // generate a send safe random 24 bytes password
        let mut rng = StdRng::from_entropy();

        // Generate a 24-byte password as a vector of bytes.
        let password_vec: Vec<u8> = (0..24).map(|_| rng.gen()).collect();
        let password = hex::encode(password_vec);

[gferon]

Fixed in 9f717c7