appsi fbbt: add tests for named expressions

[michaelbynum]

Changes proposed in this PR:

• Add a test for performing FBBT with named expressions
• Improve error messages in FBBT when a constraint is found to be infeasible

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1. I agree my contributions are submitted under the BSD license.
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[codecov]

Codecov Report

Merging #2392 (a39069c) into main (762d6ca) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2392   +/-   ##
=======================================
  Coverage   85.86%   85.86%           
=======================================
  Files         617      617           
  Lines       76163    76163           
=======================================
+ Hits        65396    65400    +4     
+ Misses      10767    10763    -4     

Flag	Coverage Δ
linux	82.60% <ø> (+<0.01%)	⬆️
osx	72.83% <ø> (ø)
other	82.79% <ø> (ø)
win	79.65% <ø> (ø)

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

Impacted Files	Coverage Δ
pyomo/contrib/mindtpy/iterate.py	83.56% <0.00%> (+1.82%)	⬆️

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