BUG: Remove array from dummy

[bashtage]

Only sparse matrices are supported so remove dense option Small typing improvement

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (f4686fa) to head (eee583c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #654      +/-   ##
==========================================
- Coverage   99.59%   99.59%   -0.01%     
==========================================
  Files          99       99              
  Lines       17335    17333       -2     
  Branches     1445     1444       -1     
==========================================
- Hits        17265    17263       -2     
  Misses         26       26              
  Partials       44       44              

Flag	Coverage Δ
adder	99.57% <100.00%> (-0.01%)	⬇️
subtractor	99.57% <100.00%> (-0.01%)	⬇️

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