update to PyO3 0.21 final

[davidhewitt]

Tidied up array parsing slightly at the same time.

[codspeed-hq]

CodSpeed Performance Report

Merging #71 will not alter performance

_{Comparing dh/pyo3-0.21 (0f80bc4) with main (2372599)}

Summary

✅ 56 untouched benchmarks

[codecov]

Codecov Report

Merging #71 (0f80bc4) into main (2372599) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #71      +/-   ##
==========================================
- Coverage   96.56%   96.54%   -0.02%     
==========================================
  Files           9        9              
  Lines        1280     1275       -5     
==========================================
- Hits         1236     1231       -5     
  Misses         44       44              

Files	Coverage Δ
src/python.rs	96.92% <100.00%> (-0.12%)	⬇️

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