pyany: add is_instance

[davidhewitt]

Adds PyAny::is_instance::<T>().

This is an alternative to Python::is_instance() which offers slightly nicer syntax. I think there's a good consistency argument to adding this:

• We expose other builtins like dir(), hash(), len() as PyAny::dir instead of Python::dir - is_instance has been a special case.
• It's also consistent with PyErr::is_instance::<T>(py).

To encourage only one way to do things, I'm very tempted to mark #[deprecated] on Python::is_instance and Python::is_subclass (which is already redundant to PyType::is_subclass). What do you think of this?

Comparing from the documentation:

Python::is_instance:

fn main() {
    let gil = Python::acquire_gil();
    let py = gil.python();
    assert!(py.is_instance::<PyBool, _>(PyBool::new(py, true)).unwrap());
    let list = PyList::new(py, &[1, 2, 3, 4]);
    assert!(!py.is_instance::<PyBool, _>(list).unwrap());
    assert!(py.is_instance::<PyList, _>(list).unwrap());
}

PyAny::is_instance:

fn main() {
    let gil = Python::acquire_gil();
    let py = gil.python();
    assert!(PyBool::new(py, true).is_instance::<PyBool>().unwrap());
    let list = PyList::new(py, &[1, 2, 3, 4]);
    assert!(!list.is_instance::<PyBool>().unwrap());
    assert!(list.is_instance::<PyList>().unwrap());
}

[davidhewitt]

cc @kngwyu - as this is a new public API that would be added to PyAny, I'd like to check you're ok with this before I merge.

[kngwyu]

Nice catch, thanks.

I'm very tempted to mark #[deprecated] on Python::is_instance and Python::is_subclass

👍