[fix][trace] log raw creation agent ingest sizes

[fankuo]

Summary

• Log creation agent input/output byte sizes at the raw IngestTraces entry point.
• Keep the TCC gate, doubao tenant restriction, and target span restriction.
• Do not log payload contents.

Validation

• go test ./modules/observability/domain/trace/service

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...bservability/domain/trace/service/trace_service.go	20.00%	11 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (33.33%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

@@           Coverage Diff           @@
##             main     #673   +/-   ##
=======================================
  Coverage   78.82%   78.82%           
=======================================
  Files         707      707           
  Lines       87823    87909   +86     
=======================================
+ Hits        69227    69295   +68     
- Misses      14607    14621   +14     
- Partials     3989     3993    +4     

Flag	Coverage Δ
unittests	78.82% <33.33%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ckend/modules/observability/application/openapi.go	86.22% <100.00%> (+0.59%)	⬆️
...bservability/domain/trace/service/trace_service.go	89.45% <20.00%> (-0.47%)	⬇️

... and 3 files with indirect coverage changes

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