Bunch of Fixes

[brendancol]

The following PR includes a bunch of fixes that I need to get CI/CD working again.

The most technically unstable is an update to experimental/polygonize.py which now has a custom implementation of generated_jit, but should in the future use nb.extends.overload style...

I also:

• got codecov working again
• added Python 3.12 support to CI/CD
• dropped 3.8 / 3.9 support from CI/CD

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.04%. Comparing base (27ab0c8) to head (a83bf9b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #796 +/- ## ========================================== + Coverage 79.94% 80.04% +0.10% ========================================== Files 19 19 Lines 4178 4179 +1 ========================================== + Hits 3340 3345 +5 + Misses 838 834 -4 ```

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