ChunkIterator: account for smaller last slice

[dmitriyrepin]

Address issue 586 Enhance ChunkIteratorV1 to make the last slice, if needed, smaller

Closes #586

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.89%. Comparing base (c3ba558) to head (6b24e35).
⚠️ Report is 184 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #702      +/-   ##
==========================================
+ Coverage   85.30%   88.89%   +3.58%     
==========================================
  Files          46       83      +37     
  Lines        2219     4466    +2247     
  Branches      306      295      -11     
==========================================
+ Hits         1893     3970    +2077     
- Misses        281      427     +146     
- Partials       45       69      +24     

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