Restore Server CPU affinity

[binaryfire]

open_cpu_affinity and cpu_affinity_ignore are still accepted and documented, but #5320 removed the code that applied them, so enabling them has had no effect since 6.0.

This restores the previous binding at the current startup points. Process-mode and base-mode event workers use the process affinity call, and reactor threads use pthread_setaffinity_np(). Thread-mode workers run in the reactor thread entry, so they are bound there instead of through the process call. Configurations that already enable open_cpu_affinity will bind workers and reactor threads again.

The regressions start a base-mode worker and a thread-mode worker with cpu_affinity_ignore set to [0] and check that each is bound to CPU 1.

[codecov]

Codecov Report

❌ Patch coverage is 68.75000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.22%. Comparing base (07606e5) to head (95c103c).

Files with missing lines	Patch %	Lines
src/server/reactor_thread.cc	66.66%	3 Missing ⚠️
src/server/master.cc	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              6.1    #6226      +/-   ##
==========================================
- Coverage   86.24%   86.22%   -0.03%     
==========================================
  Files         110      110              
  Lines       16790    16806      +16     
  Branches     2980     2986       +6     
==========================================
+ Hits        14481    14491      +10     
- Misses       2309     2315       +6     

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