[#noissue] Introduce SpanHeader enum for the trace qualifier type byte

[emeroad]

• SpanHeader enum owns the code <-> span/chunk/source-type mapping;
  decoders resolve headers via SpanHeader.of(byte)
• Add serviceUid-bearing *_UID variants so the qualifier can carry
  a serviceUid
• SpanHeaderFactory owns the write-path variant selection and the
  collector.span.serviceuid.enabled policy

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.67%. Comparing base (6d39146) to head (1e8c85c).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...er/trace/v2/config/SpanSerializeConfiguration.java	0.00%	2 Missing ⚠️
...rver/bo/serializer/trace/v2/SpanHeaderFactory.java	91.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #14049      +/-   ##
============================================
+ Coverage     34.64%   34.67%   +0.02%     
- Complexity    12300    12325      +25     
============================================
  Files          4203     4204       +1     
  Lines         99848    99874      +26     
  Branches      10695    10703       +8     
============================================
+ Hits          34594    34630      +36     
+ Misses        62313    62297      -16     
- Partials       2941     2947       +6     

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