AbstractSparseMatrixCSR interface baseline

[termi-official]

CSR interface for #538 . Don't mind the typo in the branch name and commit.

TODOs

• Increase test coverage
• Docs
• Decide what to export

[codecov]

Codecov Report

❌ Patch coverage is 33.39623% with 353 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.30%. Comparing base (313a04f) to head (01befd0).
⚠️ Report is 54 commits behind head on main.

Files with missing lines	Patch %	Lines
src/sparseconvert.jl	4.22%	136 Missing ⚠️
src/linalg.jl	35.67%	110 Missing ⚠️
src/sparsematrix.jl	50.69%	107 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #546      +/-   ##
==========================================
- Coverage   84.09%   81.30%   -2.79%     
==========================================
  Files          12       12              
  Lines        9102     9612     +510     
==========================================
+ Hits         7654     7815     +161     
- Misses       1448     1797     +349     

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