Remove some unnecessary parens when printing nonlinear expressions

[odow]

https://yetanothermathprogrammingconsultant.blogspot.com/2026/03/experience-with-nlp-solvers-on-simple.html

Obviously the superfluous parentheses are better left out. The developer was a bit lazy here.

I'll put my ✋ up for that one.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.96%. Comparing base (38f45a7) to head (081f771).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4201   +/-   ##
=======================================
  Coverage   99.96%   99.96%           
=======================================
  Files          43       43           
  Lines        6313     6315    +2     
=======================================
+ Hits         6311     6313    +2     
  Misses          2        2           

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