Update eventhandling.jl

[behinger]

This function has been around a long time, but actually never been included in Unfold.jl

Checklist

• I am following the contributing guidelines
• Tests added
• Docs/Tutorial added

[codecov]

Codecov Report

❌ Patch coverage is 0% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.37%. Comparing base (7950df6) to head (638cd1f).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/eventhandling.jl	0.00%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #247      +/-   ##
==========================================
- Coverage   63.42%   63.37%   -0.05%     
==========================================
  Files          23       23              
  Lines        1378     1379       +1     
==========================================
  Hits          874      874              
- Misses        504      505       +1     

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