fix(proto): Permissive integers in protobuf JSON parsing

[marc-pydantic]

Fixes: #3328

Changes

Ensure that we accept both u64 and String as inputs for large numbers, as the protobuf spec dictates (see #3328).

Note: This deviates in pattern slightly from established code, using a visitor for IntOrString -- I hope this is okay, but there's potential to unify here.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

(Technically it is an API change, since more values are now accepted?)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: marc-pydantic / name: Marc Brinkmann (c1587f5)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.3%. Comparing base (580633e) to head (c1587f5).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3329   +/-   ##
=====================================
  Coverage   81.3%   81.3%           
=====================================
  Files        128     128           
  Lines      23641   23641           
=====================================
+ Hits       19228   19232    +4     
+ Misses      4413    4409    -4     

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[marc-pydantic]

Had some issue with the CLA system, but these are resolved now.