ci(llmobs): add evaluation metric assertion helper using node:assert

[sabrenner]

What does this PR do?

Follow-up on #6709 to re-enable an evaluation metrics test with a new assertion helper

Motivation

Re-enable test, use node:assert instead of mocha where possible

[github-actions]

Overall package size

Self size: 4.39 MB
Deduped: 5.21 MB
No deduping: 5.21 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | import-in-the-middle | 2.0.0 | 68.46 kB | 797.03 kB | | dc-polyfill | 0.1.10 | 26.73 kB | 26.73 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.56%. Comparing base (61f0b12) to head (05cc6ae).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7227      +/-   ##
==========================================
+ Coverage   84.37%   84.56%   +0.18%     
==========================================
  Files         522      532      +10     
  Lines       22167    22651     +484     
==========================================
+ Hits        18704    19154     +450     
- Misses       3463     3497      +34     

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[pr-commenter]

Benchmarks

Benchmark execution time: 2026-01-13 15:15:57

Comparing candidate commit 05cc6ae in PR branch sabrenner/llmobs-eval-metrics-node-assert with baseline commit 61f0b12 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 291 metrics, 29 unstable metrics.