Refactor type conversions

[adrhill]

• big, widen and float now only return the promoted primal type when called on Dual
• reorganize and shorten the code for type conversions

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.28%. Comparing base (8251cb3) to head (6cdb8e1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
- Coverage   91.65%   91.28%   -0.38%     
==========================================
  Files          37       37              
  Lines        1786     1779       -7     
==========================================
- Hits         1637     1624      -13     
- Misses        149      155       +6     

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