New nrow_subset_linter

[MichaelChirico]

Part of #884

No hits on {lintr}

Will convert some of the TODOs as follow-up issues, I was surprised how many hits this simple version gets already though.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c96d024) 99.38% compared to head (8d5f852) 99.38%.

❗ Current head 8d5f852 differs from pull request most recent head 4bf5bb4. Consider uploading reports for the commit 4bf5bb4 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2298   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files         119      119           
  Lines        5392     5392           
=======================================
  Hits         5359     5359           
  Misses         33       33           

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[MichaelChirico]

Will convert the TODO to new issues after initial review to satisfy commented_code_linter().

[AshesITR]

Could use a lot more testing, especially negatives, vectorization and metadata.