[WIP] perf(telemetry): serialize batches on shared thread pool

[jpnurmi]

Warning

WIP    🚧🔨⏳⛔

• Let the telemetry module own a shared serialization pool for enabled telemetry batchers.
• Use the pool for log and metric batch serialization while keeping completion ordered through the batcher.

before-vs-after.ftrace.zip

Close: #1862

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[codecov]

Codecov Report

❌ Patch coverage is 85.97786% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.32%. Comparing base (e9a1eb3) to head (7e20632).

Additional details and impacted files

@@                     Coverage Diff                      @@
##           jpnurmi/perf/thread-pool    #1946      +/-   ##
============================================================
+ Coverage                     76.11%   76.32%   +0.21%     
============================================================
  Files                            94       94              
  Lines                         22393    22630     +237     
  Branches                       3998     4032      +34     
============================================================
+ Hits                          17045    17273     +228     
- Misses                         4459     4463       +4     
- Partials                        889      894       +5     

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[cursor]

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