Update handling of 0* in linear, quadratic walkers

[jsiirola]

Fixes # .

Summary/Motivation:

@Robbybp pointed out inconsistencies / errors in how 0* was handled for monomial, linear, quadratic, and general nonlinear terms within the Linear and Quadratic representation visitors. This PR resolves those inconsistencies and adds tests for the expected behavior.

Changes proposed in this PR:

• 0*term should result in the term being removed from the representation (for all cases of monomial, linear, quadratic, and general nonlinear)
• Add tests for this behavior.

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[blnicho]

I found one minor typo

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02% 🎉

Comparison is base (1764336) 88.06% compared to head (bb7261c) 88.08%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2981      +/-   ##
==========================================
+ Coverage   88.06%   88.08%   +0.02%     
==========================================
  Files         769      769              
  Lines       89454    89473      +19     
==========================================
+ Hits        78780    78816      +36     
+ Misses      10674    10657      -17     

Flag	Coverage Δ
linux	85.18% <100.00%> (-0.01%)	⬇️
osx	74.98% <100.00%> (-0.01%)	⬇️
other	85.35% <100.00%> (-0.01%)	⬇️
win	82.43% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
pyomo/repn/linear.py	96.47% <100.00%> (-0.58%)	⬇️
pyomo/repn/quadratic.py	91.00% <100.00%> (+0.14%)	⬆️

... and 16 files with indirect coverage changes

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