Enable integration test for Span validation

[lalitb]

• Add custom serialization for i64 as int64, fixed64, uint64 should be serialized as string in json
• Custom serialization for u64 for timestamp was added in Add custom serde encoding/decoding for timestamp #1666
• Enable integration test for Span validtion.

Changes

Please provide a brief description of the changes 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)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.6%. Comparing base (348ec9e) to head (9e9932c).
Report is 24 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1753     +/-   ##
=======================================
+ Coverage   71.0%   71.6%   +0.5%     
=======================================
  Files        135     136      +1     
  Lines      20751   20845     +94     
=======================================
+ Hits       14746   14934    +188     
+ Misses      6005    5911     -94     

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[TommyCpp]

Thanks for fixing this. Though is it expected for the OTLP collector JSON exporter to export int value to string?