fix: do not add/remove workers in debug mode

[rustatian]

Reason for This PR

• Workers should not be added in debug mode.

Description of Changes

• Restrict Add/Remove operations in debug mode.
• Correct Remove operation, remove if len > 0 check.

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 #96 (0e54ba9) into master (736fe1f) will decrease coverage by 0.40%.
The diff coverage is 0.00%.

❗ Current head 0e54ba9 differs from pull request most recent head 5c537da. Consider uploading reports for the commit 5c537da to get more accurate results

@@            Coverage Diff             @@
##           master      #96      +/-   ##
==========================================
- Coverage   77.49%   77.10%   -0.40%     
==========================================
  Files          23       23              
  Lines        2066     2070       +4     
==========================================
- Hits         1601     1596       -5     
- Misses        410      418       +8     
- Partials       55       56       +1     

Files Changed	Coverage Δ
pool/static_pool/workers_pool.go	68.35% <0.00%> (-2.39%)	⬇️
worker_watcher/worker_watcher.go	86.73% <ø> (-1.19%)	⬇️

... and 1 file with indirect coverage changes