unpack: use cextras for semaphore

[Gottox]

This replaces the use of semaphores with the cextras library. This allows support for platforms that do not provide sem_t semaphores such as OpenBSD or have deprecated them such as macOS.

[sonarcloud]

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 SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 64.37%. Comparing base (5b33483) to head (19eeca4).
Report is 2 commits behind head on main.

Files	Patch %	Lines
tools/src/unpack.c	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #285   +/-   ##
=======================================
  Coverage   64.37%   64.37%           
=======================================
  Files          75       75           
  Lines        5752     5752           
  Branches      874      874           
=======================================
  Hits         3703     3703           
  Misses       1531     1531           
  Partials      518      518           

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