Fix event weights in weighted reflectivity calculation

[mdoucet]

One option for normalization when computing R is to assign a weight to each event according to the flux spectrum. This allows to bin easily in Q, Qx-Qz, etc.. The implementation didn't account for the recent addition of the dead time correction.
This PR fixes that.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 83.31%. Comparing base (b664256) to head (4ba6c18).
Report is 23 commits behind head on next.

Files with missing lines	Patch %	Lines
reduction/lr_reduction/event_reduction.py	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next      #52      +/-   ##
==========================================
- Coverage   83.87%   83.31%   -0.57%     
==========================================
  Files          20       20              
  Lines        2431     2451      +20     
==========================================
+ Hits         2039     2042       +3     
- Misses        392      409      +17     

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