Introduce CartesianPair

[mtfishman]

Supersedes #24.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 24 lines in your changes missing coverage. Please review.

Project coverage is 78.91%. Comparing base (1cd2ce3) to head (06c3e30).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cartesianproduct.jl	70.58%	10 Missing ⚠️
src/kroneckerarray.jl	75.60%	10 Missing ⚠️
...seArraysExt/KroneckerArraysBlockSparseArraysExt.jl	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   79.85%   78.91%   -0.95%     
==========================================
  Files          11       11              
  Lines         695      716      +21     
==========================================
+ Hits          555      565      +10     
- Misses        140      151      +11     

Flag	Coverage Δ
docs	0.00% <0.00%> (ø)

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