metricdatatest: support BYTESLICE attribute comparisons

[pellared]

Address #7948 (comment)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.3%. Comparing base (112bed7) to head (05ec79a).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #8167   +/-   ##
=====================================
  Coverage   82.2%   82.3%           
=====================================
  Files        309     309           
  Lines      24211   24214    +3     
=====================================
+ Hits       19906   19932   +26     
+ Misses      3927    3904   -23     
  Partials     378     378           

Files with missing lines	Coverage Δ
...dk/metric/metricdata/metricdatatest/comparisons.go	97.4% <100.0%> (+4.7%)	⬆️

... and 3 files with indirect coverage changes

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