Use atomic operations for single value counters

[gammazero]

This is much faster than using mutexes when used for single values. When synchronizing single values, generally atomic variables are preferred.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2d540e3) 74.02% compared to head (f549d4a) 73.90%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
- Coverage   74.02%   73.90%   -0.12%     
==========================================
  Files         149      149              
  Lines        9823     9816       -7     
==========================================
- Hits         7271     7255      -16     
- Misses       1802     1808       +6     
- Partials      750      753       +3     

Files	Coverage Δ
service/dealtracker/countreader.go	82.35% <100.00%> (-5.15%)	⬇️

... and 3 files with indirect coverage changes

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