metrics: use atomic type

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #1504 (0e2bc5f) into master (51b6aae) will increase coverage by 0.05%.
The diff coverage is 88.00%.

❗ Current head 0e2bc5f differs from pull request most recent head 34ea155. Consider uploading reports for the commit 34ea155 to get more accurate results

@@            Coverage Diff             @@
##           master    #1504      +/-   ##
==========================================
+ Coverage   52.13%   52.18%   +0.05%     
==========================================
  Files         474      474              
  Lines       59511    59517       +6     
==========================================
+ Hits        31025    31058      +33     
+ Misses      26132    26114      -18     
+ Partials     2354     2345       -9     

Impacted Files	Coverage Δ
params/version.go	33.33% <ø> (ø)
metrics/gauge.go	44.64% <60.00%> (ø)
metrics/counter.go	38.77% <83.33%> (ø)
metrics/ewma.go	67.56% <100.00%> (ø)
metrics/meter.go	68.93% <100.00%> (+1.47%)	⬆️

... and 15 files with indirect coverage changes