snipe off some unsafe code

[davidhewitt]

Change Summary

The goal here is to remove all uses of unsafe which I could replace with safe code, or alternatively justify with a Safety comment. The changes make use of safe abstractions which should completely optimize away (especially with full LTO) so no performance impact is expected.

The only exception is that there were some uses of PyByteArray::as_bytes which I didn't agree with as appropriate, and I copied the output of those cases into a new allocation. This is a necessary performance loss in exchange for correctness.

Related issue number

Related to pydantic/pydantic#7211 - doing some due diligence here felt worthwhile.

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

[codecov]

Codecov Report

Merging #922 (0a93ee4) into main (882b57f) will decrease coverage by 0.02%.
The diff coverage is 78.31%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #922      +/-   ##
==========================================
- Coverage   93.84%   93.82%   -0.02%     
==========================================
  Files         105      105              
  Lines       15459    15436      -23     
  Branches       25       25              
==========================================
- Hits        14507    14483      -24     
- Misses        946      947       +1     
  Partials        6        6              

Files Changed	Coverage Δ
src/serializers/infer.rs	95.00% <44.44%> (-0.74%)	⬇️
src/input/return_enums.rs	85.29% <53.84%> (-0.30%)	⬇️
src/errors/validation_exception.rs	93.68% <95.00%> (-0.16%)	⬇️
src/input/input_python.rs	98.29% <100.00%> (-0.01%)	⬇️
src/serializers/ob_type.rs	80.80% <100.00%> (-0.08%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #922 will not alter performance

_{Comparing dh/safer (0a93ee4) with main (882b57f)}

Summary

✅ 138 untouched benchmarks

[davidhewitt]

Integration test failures are due to #911

[davidhewitt]

please review