Update PyO3 to 0.20

[davidhewitt]

Change Summary

Updates PyO3 to 0.20.

(For now in draft and building against the git dependency, will update this when the release is done.)

Related issue number

Fixes #761
Fixes pydantic/pydantic#6584

Checklist

• Unit tests for the changes exist
• Documentation reflects the changes where applicable
• Pydantic tests pass with this pydantic-core (except for expected changes)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @samuelcolvin

[davidhewitt]

By far the bulk of the work is migrating for https://pyo3.rs/main/migration.html#pydictget_item-now-returns-a-result

[codecov]

Codecov Report

Merging #1003 (cff1afe) into main (b51105a) will decrease coverage by 0.01%.
The diff coverage is 96.36%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1003      +/-   ##
==========================================
- Coverage   93.06%   93.05%   -0.01%     
==========================================
  Files         106      106              
  Lines       15739    15720      -19     
  Branches       35       35              
==========================================
- Hits        14648    14629      -19     
  Misses       1084     1084              
  Partials        7        7              

Files	Coverage Δ
src/errors/types.rs	99.66% <100.00%> (ø)
src/errors/validation_exception.rs	91.60% <100.00%> (ø)
src/errors/value_exception.rs	89.65% <ø> (ø)
src/input/input_python.rs	98.36% <ø> (ø)
src/input/return_enums.rs	84.93% <ø> (ø)
src/lookup_key.rs	92.65% <100.00%> (ø)
src/serializers/extra.rs	99.08% <ø> (ø)
src/serializers/filter.rs	96.06% <100.00%> (-0.02%)	⬇️
src/serializers/type_serializers/dict.rs	95.55% <100.00%> (ø)
src/serializers/type_serializers/model.rs	94.55% <100.00%> (ø)
... and 21 more

---

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[codspeed-hq]

CodSpeed Performance Report

Merging #1003 will improve performances by 28.87%

_{Comparing dh/pyo3-0.20 (cff1afe) with main (b51105a)}

Summary

⚡ 1 improvements
✅ 139 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	dh/pyo3-0.20	Change
⚡	test_decimal_from_string_core	70 µs	54.3 µs	+28.87%

[davidhewitt]

please review

[PrettyWood]

LGTM

[PrettyWood]

I didn't see what forced this change from [pyo3 changelog]

[davidhewitt]

I believe it was the switch to syn 2.0 changing the way the proc macro parsed idents.