[CODE HEALTH] Move trace and baggage propagation test classes into anonymous namespace

[mateenali66]

Moves the TextMapCarrierTest helper in the b3, http_text_format and jaeger trace propagation tests, and BaggageCarrierTest in the baggage propagation test, into anonymous namespaces, resolving their misc-use-internal-linkage clang-tidy warnings. Test-only, no behavior change.

Lowered the clang-tidy warning_limit by 4 for both ABI presets accordingly.

Part of #4196.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.90%. Comparing base (a56f0e2) to head (cd33fb0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4199      +/-   ##
==========================================
+ Coverage   82.89%   82.90%   +0.01%     
==========================================
  Files         405      405              
  Lines       17292    17289       -3     
==========================================
- Hits        14332    14331       -1     
+ Misses       2960     2958       -2     

see 1 file with indirect coverage changes

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[thc1006]

These look clean. One cross-PR heads-up since #4199 and #4200 overlap on the ratchet file: both lower warning_limit in clang-tidy.yaml from the same base (328 abiv1, 338 abiv2) while touching disjoint test files (#4199 removes 4 warnings, #4200 removes 3). So whichever merges first, the other will hit a merge conflict on those two lines and need a quick rebase. After both land the combined value should be 321 and 331 (328 and 338, each minus 7). Flagging it so the second one is not accidentally left at its single-PR number (324/334 or 325/335), which would leave the ceiling looser than the actual count.

[dbarker]

Thanks!

[marcalff]

LGTM