feat: improve outbound_dropped_messages metric

[denopink]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 70.49180% with 90 lines in your changes are missing coverage. Please review.

Project coverage is 59.90%. Comparing base (dca746e) to head (e5d8547).
Report is 13 commits behind head on main.

Files	Patch %	Lines
workerPool.go	44.26%	22 Missing and 12 partials ⚠️
eventDispatcher.go	73.91%	20 Missing and 10 partials ⚠️
metrics.go	78.51%	20 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #391      +/-   ##
==========================================
+ Coverage   59.88%   59.90%   +0.02%     
==========================================
  Files          18       18              
  Lines        1558     1776     +218     
==========================================
+ Hits          933     1064     +131     
- Misses        611      671      +60     
- Partials       14       41      +27     

Flag	Coverage Δ
unittests	59.90% <70.49%> (+0.02%)	⬆️

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