Fix q-summing for up/down reflection

[mdoucet]

The way we compute the q offset according to counts in pixels in y needs to account for whether we reflect up or down. This PR fixes that.

For a correct calculation, we also need the reflected peak's true center, not just the center of the range.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 23.80952% with 16 lines in your changes missing coverage. Please review.

Project coverage is 83.41%. Comparing base (b664256) to head (8f850aa).
Report is 9 commits behind head on next.

Files with missing lines	Patch %	Lines
reduction/lr_reduction/event_reduction.py	16.66%	10 Missing ⚠️
reduction/lr_reduction/template.py	33.33%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next      #51      +/-   ##
==========================================
- Coverage   83.87%   83.41%   -0.46%     
==========================================
  Files          20       20              
  Lines        2431     2448      +17     
==========================================
+ Hits         2039     2042       +3     
- Misses        392      406      +14     

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