pyo3 0.16.3

Thank you for contributing to pyo3!

Please consider adding the following to your pull request:
 - an entry in CHANGELOG.md
 - docs to all new functions and / or detail in the guide
 - tests for all new or changed functions

PyO3's CI pipeline will check your pull request. To run its tests
locally, you can run ```cargo xtask ci```. See its documentation
 [here](https://github.com/PyO3/pyo3/tree/main/xtask#readme).