Update PyO3 to 0.22 (#1293)

* Prototype of migration (pt1)

* Temporarily remove Slicing because I want to handle it later

* Cargo fmt

* Tackle first batch of warnings

* Second batch for warning fixes

* Third batch of warning fixes

* Final batch of warning fixes

* Re-introduce slicing support

* Update ndarray as well

* Use NumPy from release

* Remove stray comment

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Co-authored-by: Matthew Treinish <mtreinish@kortar.org>