Keep track of expected number of margin rows written.

[delucchi-cmu]

Closes #258.

As a bonus, we can track the number of rows that are expected from the mapping stage, and we can double-check total after reducing stage.

[codecov]

Codecov Report

Attention: Patch coverage is 91.11111% with 4 lines in your changes missing coverage. Please review.

Project coverage is 98.63%. Comparing base (f455690) to head (d302ade).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...ts_import/margin_cache/margin_cache_resume_plan.py	88.88%	2 Missing ⚠️
src/hats_import/margin_cache/margin_cache.py	85.71%	1 Missing ⚠️
src/hats_import/pipeline_resume_plan.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
- Coverage   98.85%   98.63%   -0.23%     
==========================================
  Files          28       28              
  Lines        1576     1615      +39     
==========================================
+ Hits         1558     1593      +35     
- Misses         18       22       +4     

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[github-actions]

Before [f455690]	After [2ef70e3]	Ratio	Benchmark (Parameter)
failed	failed	n/a	benchmarks.BinningSuite.time_read_histogram

Click here to view all benchmarks.

[gitosaurus]

Looks good! Tiny stylistic comments only.