Support evaluating PiecewiseLinearExpression objects

[jsiirola]

Fixes # .

Summary/Motivation:

This resolves an oversight where expressions containing PiecewiseLinearExpression objects could bot be evaluated (e.g., using value())

Changes proposed in this PR:

• Add support for evaluating PiecewiseLinearExpression
• Remove redundant method definition
• Add additional testing

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.94%. Comparing base (5c1ca8c) to head (fee4097).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4007   +/-   ##
=======================================
  Coverage   89.93%   89.94%           
=======================================
  Files         917      917           
  Lines      109101   109101           
=======================================
+ Hits        98124    98130    +6     
+ Misses      10977    10971    -6     

Flag	Coverage Δ
builders	29.08% <50.00%> (-0.01%)	⬇️
default	86.13% <100.00%> (?)
expensive	35.07% <50.00%> (?)
linux	87.67% <100.00%> (-1.98%)	⬇️
linux_other	87.67% <100.00%> (+<0.01%)	⬆️
oldsolvers	27.56% <50.00%> (+<0.01%)	⬆️
osx	83.11% <100.00%> (+<0.01%)	⬆️
win	85.43% <100.00%> (+0.01%)	⬆️

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