chore: worker_watcher refactoring

[rustatian]

Reason for This PR

closes: roadrunner-server/roadrunner#1180

Description of Changes

• Refactor worker_watcher, and remove unused or misused features.
• Prevent from allocating zombie processes.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The reason for this PR is clearly provided (issue no. or explanation).
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.

[codecov]

Codecov Report

Merging #36 (f5db2a6) into master (b9bf72a) will increase coverage by 0.32%.
The diff coverage is 56.62%.

@@            Coverage Diff             @@
##           master      #36      +/-   ##
==========================================
+ Coverage   77.83%   78.15%   +0.32%     
==========================================
  Files          23       24       +1     
  Lines        2161     2129      -32     
==========================================
- Hits         1682     1664      -18     
+ Misses        398      382      -16     
- Partials       81       83       +2     

Impacted Files	Coverage Δ
pool/options.go	0.00% <ø> (ø)
pool/allocator.go	86.84% <28.57%> (-13.16%)	⬇️
worker_watcher/container/channel/vec.go	76.76% <33.33%> (-2.81%)	⬇️
worker_watcher/worker_watcher.go	81.74% <47.36%> (+0.61%)	⬆️
pool/errEncoder.go	55.26% <55.26%> (ø)
ipc/pipe/pipe_factory.go	76.28% <100.00%> (+0.75%)	⬆️
pool/static_pool.go	70.52% <100.00%> (+2.12%)	⬆️
pool/stream_pool.go	65.09% <100.00%> (+2.33%)	⬆️
worker/sync_worker.go	80.00% <100.00%> (+0.09%)	⬆️
worker/worker.go	84.61% <100.00%> (ø)
... and 2 more

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