GDP: Fix performance degredation in hull transformation

[emma58]

Fixes # .

Summary/Motivation:

In #3143, I accidentally introduced a performance degradation into gdp.hull because of using a Reference over a slice in order to map from disaggregated variables to the bound constraints for them. This PR eliminates the use of Reference, taking the hull transformation time on one model down from 150 seconds to 50 seconds.

NOTE: this includes #3365 in an attempt to get tests passing

Changes proposed in this PR:

• Move the logic for mapping from disaggregated variables to their bound constraints to the _declare_disaggregated_var_bounds helper method that actually knows whether we have both lower and upper bounds for the variables.
• No longer using the same keys in the _boundConstraints component on the transformation Block as we do in the mappings--the mappings can be pretty and simple ('lb' and 'ub') since they end up public-facing via the get_var_bounds_constraint method whereas the actual keys in _boundsConstraints can be ugly and unique.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.63%. Comparing base (b983b91) to head (149691a).
Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3366      +/-   ##
==========================================
- Coverage   88.63%   88.63%   -0.01%     
==========================================
  Files         879      879              
  Lines      100221   100227       +6     
==========================================
- Hits        88834    88833       -1     
- Misses      11387    11394       +7     

Flag	Coverage Δ
linux	86.27% <100.00%> (+<0.01%)	⬆️
osx	75.64% <100.00%> (+<0.01%)	⬆️
other	86.76% <100.00%> (+<0.01%)	⬆️
win	84.02% <100.00%> (+<0.01%)	⬆️

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