Enforce MKL interface limits

[mdekstrand]

This PR checks and enforces limits on the MKL interfaces, and adds data transformations to ensure that it works when possible.

The MKL kernel cannot handle matrices with more than INT_MAX nonzero elements. We now have much better checking, along with utility methods and logic to help with this enforcement and appropriate data transformations.

[codecov]

Codecov Report

Merging #10 (4b5c0c9) into main (75bb97e) will decrease coverage by 1.28%.
The diff coverage is 80.35%.

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
- Coverage   95.51%   94.23%   -1.29%     
==========================================
  Files          19       19              
  Lines         981     1023      +42     
==========================================
+ Hits          937      964      +27     
- Misses         44       59      +15     

Impacted Files	Coverage Δ
csr/csr.py	95.14% <77.27%> (-3.56%)	⬇️
csr/kernels/mkl/handle.py	92.47% <78.57%> (-6.18%)	⬇️
csr/_struct.py	82.35% <100.00%> (+3.78%)	⬆️

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