Not possible to use multiple operators to same observable

[aleics]

Since Observable does not implement the copy trait, it's currently not possible to use multiple operators.

Example:

#[test]
fn multiple_operators_same_observable() {
    let observable = of(&[1, 2 ,3]);

    let even = observable.filter(|item| item % 2 == 0);
    let odd = observable.filter(|item| item % 2 == 1);

    assert!(values_sent(&even, &[2]));
    assert!(is_completed(&even));
    assert!(values_sent(&odd, &[1, 3]));
    assert!(is_completed(&odd));
}