[feat][backend] trace oapi support original tag

[cuichen01]

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[CozeLoop]

Code review comments added focusing on original tag propagation and map aliasing risks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #303      +/-   ##
==========================================
+ Coverage   68.44%   68.52%   +0.08%     
==========================================
  Files         569      569              
  Lines       51765    51775      +10     
==========================================
+ Hits        35432    35481      +49     
+ Misses      13582    13555      -27     
+ Partials     2751     2739      -12     

Flag	Coverage Δ
unittests	68.52% <100.00%> (+0.08%)	⬆️

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Files with missing lines	Coverage Δ
.../observability/application/convertor/trace/span.go	82.03% <100.00%> (+25.98%)	⬆️
...ckend/modules/observability/application/openapi.go	74.68% <100.00%> (ø)
backend/modules/observability/application/trace.go	69.42% <100.00%> (ø)

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