IntoPyCallbackOutput<_> is not implimented for arrays of pyclass

[andyblarblar]

Bug Description

I'm attempting to use a pyclass annotated struct array as the member of another pyclass annotated struct. When I attempt to annotate that array feild with pyo3(get), it fails to compile. I'm building off of the current master (dea9eb7) as it's latest commit seems to cover this use case.

Steps to Reproduce

Minimal example:

#[pyclass]
#[derive(Copy, Clone)]
struct Foo {
    x: i32
}

#[pyclass]
struct Bar {
    #[pyo3(get)]
    arr: [Foo; 12]
}

Backtrace

error[E0277]: the trait bound `[Foo; 12]: IntoPyCallbackOutput<_>` is not satisfied
   --> src/ld06_driver.rs:21:1
    |
21  | #[pyclass]
    | ^^^^^^^^^^ the trait `IntoPyCallbackOutput<_>` is not implemented for `[Foo; 12]`
    |
    = help: the following other types implement trait `IntoPyCallbackOutput<Target>`:
              <() as IntoPyCallbackOutput<()>>
              <() as IntoPyCallbackOutput<i32>>
              <*mut PyObject as IntoPyCallbackOutput<*mut PyObject>>
              <HashCallbackOutput as IntoPyCallbackOutput<isize>>
              <IterANextOutput<Py<PyAny>, Py<PyAny>> as IntoPyCallbackOutput<*mut PyObject>>
              <IterANextOutput<T, U> as IntoPyCallbackOutput<IterANextOutput<Py<PyAny>, Py<PyAny>>>>
              <IterNextOutput<Py<PyAny>, Py<PyAny>> as IntoPyCallbackOutput<*mut PyObject>>
              <IterNextOutput<T, U> as IntoPyCallbackOutput<IterNextOutput<Py<PyAny>, Py<PyAny>>>>
            and 7 others
note: required by a bound in `pyo3::callback::convert`
   --> /home/andy/.cargo/git/checkouts/pyo3-a22e69bc62b9f0fd/dea9eb7/src/callback.rs:182:8
    |
182 |     T: IntoPyCallbackOutput<U>,
    |        ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `pyo3::callback::convert`

### Your operating system and version

Ubuntu 20.04

### Your Python version (`python --version`)

Python 3.8

### Your Rust version (`rustc --version`)

rustc 1.60.0 (7737e0b5c 2022-04-04)

### Your PyO3 version

dea9eb7a master

### How did you install python? Did you use a virtualenv?

apt

### Additional Info

_No response_

[mejrs]

You just need to add this implementation to make it work:

impl ToPyObject for Foo{
    fn to_object(&self, py: Python<'_>) -> PyObject{
        self.into_py(py)
    }
}

This error is actually really bad - I'd like to improve it.

[mejrs]

Actually, I think I can make this work without requiring ToPyObject

[mejrs]

I'm building off of the current master (dea9eb7) as it's latest commit seems to cover this use case.

That commit addresses the case of references to arrays, so it doesn't help here. However #2326 does :)