chore: Move to dispatch conditions / NIOLock instead of raw pthread mutex/conditions

[hassila]

Fixes #21

Basically borrowed NIOLock for the time being until we have some other native swift concurrency primitive for synchronisation, using dispatch semaphores instead of pthread ones.

[codecov]

Codecov Report

Merging #39 (cab6379) into main (b7e7a19) will decrease coverage by 0.24%.
The diff coverage is 88.57%.

❗ Current head cab6379 differs from pull request most recent head d21c581. Consider uploading reports for the commit d21c581 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   83.59%   83.36%   -0.24%     
==========================================
  Files          19       20       +1     
  Lines        2200     2241      +41     
==========================================
+ Hits         1839     1868      +29     
- Misses        361      373      +12     

Impacted Files	Coverage Δ
...s/BenchmarkSupport/BenchmarkRunner+ReadWrite.swift	57.14% <ø> (ø)
Sources/BenchmarkSupport/NIOLock.swift	74.19% <74.19%> (ø)
Sources/Benchmark/Benchmark.swift	82.24% <100.00%> (-0.54%)	⬇️
...ort/MallocStats/MallocStatsProducer+jemalloc.swift	76.14% <100.00%> (ø)
...stemStats/OperatingSystemStatsProducer+Linux.swift	95.56% <100.00%> (+1.23%)	⬆️

Impacted Files	Coverage Δ
...s/BenchmarkSupport/BenchmarkRunner+ReadWrite.swift	57.14% <ø> (ø)
Sources/BenchmarkSupport/NIOLock.swift	74.19% <74.19%> (ø)
Sources/Benchmark/Benchmark.swift	82.24% <100.00%> (-0.54%)	⬇️
...ort/MallocStats/MallocStatsProducer+jemalloc.swift	76.14% <100.00%> (ø)
...stemStats/OperatingSystemStatsProducer+Linux.swift	95.56% <100.00%> (+1.23%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b7e7a19...d21c581. Read the comment docs.