Set up package extensions, improve permutedims

[mtfishman]

Closes #6.

[codecov]

Codecov Report

Attention: Patch coverage is 51.85185% with 13 lines in your changes missing coverage. Please review.

Project coverage is 27.27%. Comparing base (d1958cc) to head (c9702e7).

Files with missing lines	Patch %	Lines
...sorAlgebraExt/BlockSparseArraysTensorAlgebraExt.jl	0.00%	7 Missing ⚠️
...ksparsearrayinterface/blocksparsearrayinterface.jl	66.66%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
+ Coverage   26.58%   27.27%   +0.69%     
==========================================
  Files          27       26       -1     
  Lines         854      869      +15     
==========================================
+ Hits          227      237      +10     
- Misses        627      632       +5     

Flag	Coverage Δ
docs	27.18% <51.85%> (+0.78%)	⬆️

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