Implement ExactSizeIterator for ArrayWindows<I, N> for small positive N

[ronnodas]

See #1117.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.92%. Comparing base (6814180) to head (8fa10a3).
⚠️ Report is 211 commits behind head on master.

Files with missing lines	Patch %	Lines
src/array_impl.rs	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1118      +/-   ##
==========================================
- Coverage   94.38%   93.92%   -0.47%     
==========================================
  Files          48       52       +4     
  Lines        6665     6687      +22     
==========================================
- Hits         6291     6281      -10     
- Misses        374      406      +32     

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