0.17.0 and 0.16.6 releases

[davidhewitt]

In #2481 we agreed that we'll need to have a "soundness" release 0.16.6 (with drawbacks) as well as a new 0.17.0 release ASAP which offers a fixed PyCapsule API.

I think this is everything which should happen for us to be ready to release:

• Finish new PyCapsule API types: rework PyCapsule for soundness #2485
• Write 0.16.6 patch for PyCapsule as per security: fix use-after-free in PyCapsule implementation #2481 (comment)
• Get pyo3-ffi-check CI green (needs some fixes for PyPy and 3.11 beta)
• Finish Update PyTryFrom for PyMapping and PySequence to more accurately check types #2477
• Implement PyClass Sequence of tuples or arrays not convertible to numpy array #2392 (comment)
• Fix for run_closure and drop_closure unsoundly drop payload on panic #2501
• Finish refactor: remove all 0.15 deprecations #2283

There are also a few other open PRs & issues I've left in the 0.17 milestone. It's fine for those to also be completed while we're tidying the release.