Fix reading of central trigger object in case of new mono trigger

[maxnoe]

The code made the assumption that the trigger mask is stored as a "normal" 8-bit unsigned integer instead of a variable length unsigned integer.

This assumption was always valid until now, but the new mono trigger requires correctly reading the masks as variable length integers.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (94ebedd) 86.40% compared to head (8dd2e4a) 86.46%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #262      +/-   ##
==========================================
+ Coverage   86.40%   86.46%   +0.05%     
==========================================
  Files          24       24              
  Lines        2192     2201       +9     
==========================================
+ Hits         1894     1903       +9     
  Misses        298      298              

Files	Coverage Δ
src/eventio/simtel/objects.py	81.20% <100.00%> (+0.17%)	⬆️

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[orelgueta]

Thanks @maxnoe!

I cannot claim to understand every line of new code added, but what I do follow looks good and I can confirm the code works with the files I simulated (with and without mono trigger).