chore: consolidate test and benchmark code

[mccutchen]

No functional changes, just moving deck chairs

[github-actions]

🔥 Run benchmarks comparing 7540641 against main:

gh workflow run bench.yaml -f pr_number=43

Note: this comment will update with each new commit.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.37%. Comparing base (e346ea9) to head (7540641).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #43   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files           3        2    -1     
  Lines         459      459           
=======================================
  Hits          424      424           
  Misses         28       28           
  Partials        7        7           

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