Fix regression that did not trigger events in nested calls within an already running transition

[fgmacedo]

• chore: Processing block protected by a threading.Lock
• fix: Regression that did not trigger events in nested calls within an already running transition. Closes Error when invoking send in sequence within on_enter_state synchronously #449

[sonarqubecloud]

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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (af78785) to head (d6e73e6).
Report is 31 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop      #451   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines         1270      1276    +6     
  Branches       190       191    +1     
=========================================
+ Hits          1270      1276    +6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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