Improving PropDiffN performance

[ArthurGodet]

Fixes # .

Changes proposed in this PR:

• Improving PropDiffN performance by changing some data structure and slightly improving energy check

@chocoteam/core-developer

[codecov-io]

Codecov Report

Merging #663 into master will increase coverage by <.01%.
The diff coverage is 81.48%.

@@             Coverage Diff              @@
##             master     #663      +/-   ##
============================================
+ Coverage     62.28%   62.29%   +<.01%     
- Complexity     9886     9896      +10     
============================================
  Files           634      634              
  Lines         40183    40199      +16     
  Branches       7686     7690       +4     
============================================
+ Hits          25027    25040      +13     
- Misses        12879    12882       +3     
  Partials       2277     2277

Impacted Files	Coverage Δ	Complexity Δ
...chocosolver/solver/variables/IVariableFactory.java	73.07% <100%> (+3.79%)	81 <5> (+5)	⬆️
...in/java/org/chocosolver/solver/variables/Task.java	80.64% <78.26%> (+0.64%)	21 <13> (+11)	⬆️
...java/org/chocosolver/solver/ParallelPortfolio.java	72.09% <0%> (-3.49%)	48% <0%> (-2%)
...cosolver/solver/constraints/ternary/PropMinBC.java	75.3% <0%> (-1.24%)	27% <0%> (-3%)
.../strategy/assignments/DecisionOperatorFactory.java	59.64% <0%> (+1.75%)	6% <0%> (ø)	⬇️

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[cprudhom]

Could you remind me the gain observed ?

[ArthurGodet]

The gain on pure random instances was about 20% faster execution for the same number of nodes for the same search strategy (inputOrder).