Validate base64 standard encoding

[josh-newman]

Change Summary

Extends bytes base64 validation to accept standard encoding, in addition to the existing URL-safe.

I think a user providing base64 standard input is more likely to want successful (and unambiguous) decoding rather than a validation error. (Even while ser_json_bytes="base64" continues to emit the URL-safe variant.)

Related issue number

No issue, but this extends #1308: #1308 (comment)

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: @dmontagu

[josh-newman]

please review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.61%. Comparing base (ab503cb) to head (f7170c5).
Report is 139 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1395      +/-   ##
==========================================
- Coverage   90.21%   89.61%   -0.60%     
==========================================
  Files         106      109       +3     
  Lines       16339    17308     +969     
  Branches       36       41       +5     
==========================================
+ Hits        14740    15511     +771     
- Misses       1592     1777     +185     
- Partials        7       20      +13     

Files	Coverage Δ
src/validators/config.rs	100.00% <100.00%> (ø)

... and 39 files with indirect coverage changes

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[codspeed-hq]

CodSpeed Performance Report

Merging #1395 will not alter performance

_{Comparing d8e-ai:validate-base64-any (f7170c5) with main (6e96b85)}

Summary

✅ 155 untouched benchmarks

[davidhewitt]

Thanks, feature design and implementation looks good to me!