[Bridges] improve function getter of SplitHyperRectangleBridge

[odow]

This avoids adding and subtracting 0 to avoid terms like +(-(+(x), 0), 0)

Before

julia> include("/Users/oscar/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl")
WARNING: replacing module TestConstraintHyperRectangle.
test_basic_HyperRectangle: Test Failed at /Users/oscar/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:268
  Expression: isapprox(MOI.Utilities.canonical(f), constraint_function, config)
   Evaluated: isapprox(┌                                                                                                           ┐
│+(-(+(^(MOI.VariableIndex(1), (2)), ^(MOI.VariableIndex(2), (2)), ^(MOI.VariableIndex(3), (2))), 0.0), 0.0)│
│+(-(+(MOI.VariableIndex(2)), 0.0), 0.0)                                                                    │
│+(-(+(MOI.VariableIndex(3)), 0.0), 0.0)                                                                    │
└                                                                                                           ┘, ┌                                                                                           ┐
│+(^(MOI.VariableIndex(1), (2)), ^(MOI.VariableIndex(2), (2)), ^(MOI.VariableIndex(3), (2)))│
│+(MOI.VariableIndex(2))                                                                    │
│+(MOI.VariableIndex(3))                                                                    │
└                                                                                           ┘, MathOptInterface.Test.Config{Float64}(1.4901161193847656e-8, 1.4901161193847656e-8, MathOptInterface.OPTIMAL, MathOptInterface.INFEASIBLE, Any[]))

Stacktrace:
 [1] macro expansion
   @ ~/.julia/juliaup/julia-1.10.8+0.x64.apple.darwin14/share/julia/stdlib/v1.10/Test/src/Test.jl:672 [inlined]
 [2] _basic_constraint_test_helper(model::MathOptInterface.Bridges.Constraint.SingleBridgeOptimizer{MathOptInterface.Bridges.Constraint.SplitHyperRectangleBridge{Float64}, MathOptInterface.Utilities.Model{Float64}}, config::MathOptInterface.Test.Config{Float64}, ::Type{MathOptInterface.VectorNonlinearFunction}, ::Type{MathOptInterface.HyperRectangle}, add_variables_fn::typeof(MathOptInterface.add_variables))
   @ MathOptInterface.Test ~/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:268
 [3] _basic_constraint_test_helper
   @ ~/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:219 [inlined]
 [4] test_basic_VectorNonlinearFunction_HyperRectangle
   @ ~/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:403 [inlined]
 [5] test_basic_HyperRectangle()
   @ Main.TestConstraintHyperRectangle ~/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:129
 [6] macro expansion
   @ ~/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:17 [inlined]
 [7] macro expansion
   @ ~/.julia/juliaup/julia-1.10.8+0.x64.apple.darwin14/share/julia/stdlib/v1.10/Test/src/Test.jl:1577 [inlined]
 [8] runtests()
   @ Main.TestConstraintHyperRectangle ~/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:17
test_basic_HyperRectangle: Test Failed at /Users/oscar/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:269
  Expression: isapprox(MOI.get(model, MOI.CanonicalConstraintFunction(), c), constraint_function, config)
   Evaluated: isapprox(┌                                                                                                           ┐
│+(-(+(^(MOI.VariableIndex(1), (2)), ^(MOI.VariableIndex(2), (2)), ^(MOI.VariableIndex(3), (2))), 0.0), 0.0)│
│+(-(+(MOI.VariableIndex(2)), 0.0), 0.0)                                                                    │
│+(-(+(MOI.VariableIndex(3)), 0.0), 0.0)                                                                    │
└                                                                                                           ┘, ┌                                                                                           ┐
│+(^(MOI.VariableIndex(1), (2)), ^(MOI.VariableIndex(2), (2)), ^(MOI.VariableIndex(3), (2)))│
│+(MOI.VariableIndex(2))                                                                    │
│+(MOI.VariableIndex(3))                                                                    │
└                                                                                           ┘, MathOptInterface.Test.Config{Float64}(1.4901161193847656e-8, 1.4901161193847656e-8, MathOptInterface.OPTIMAL, MathOptInterface.INFEASIBLE, Any[]))

Stacktrace:
 [1] macro expansion
   @ ~/.julia/juliaup/julia-1.10.8+0.x64.apple.darwin14/share/julia/stdlib/v1.10/Test/src/Test.jl:672 [inlined]
 [2] _basic_constraint_test_helper(model::MathOptInterface.Bridges.Constraint.SingleBridgeOptimizer{MathOptInterface.Bridges.Constraint.SplitHyperRectangleBridge{Float64}, MathOptInterface.Utilities.Model{Float64}}, config::MathOptInterface.Test.Config{Float64}, ::Type{MathOptInterface.VectorNonlinearFunction}, ::Type{MathOptInterface.HyperRectangle}, add_variables_fn::typeof(MathOptInterface.add_variables))
   @ MathOptInterface.Test ~/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:269
 [3] _basic_constraint_test_helper
   @ ~/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:219 [inlined]
 [4] test_basic_VectorNonlinearFunction_HyperRectangle
   @ ~/.julia/dev/MathOptInterface/src/Test/test_basic_constraint.jl:403 [inlined]
 [5] test_basic_HyperRectangle()
   @ Main.TestConstraintHyperRectangle ~/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:129
 [6] macro expansion
   @ ~/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:17 [inlined]
 [7] macro expansion
   @ ~/.julia/juliaup/julia-1.10.8+0.x64.apple.darwin14/share/julia/stdlib/v1.10/Test/src/Test.jl:1577 [inlined]
 [8] runtests()
   @ Main.TestConstraintHyperRectangle ~/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:17
Test Summary:             | Pass  Fail  Total  Time
test_basic_HyperRectangle |   89     2     91  2.1s
ERROR: LoadError: Some tests did not pass: 89 passed, 2 failed, 0 errored, 0 broken.
in expression starting at /Users/oscar/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl:135

After

julia> include("/Users/oscar/.julia/dev/MathOptInterface/test/Bridges/Constraint/SplitHyperRectangleBridge.jl")
WARNING: replacing module TestConstraintHyperRectangle.
Test Summary:             | Pass  Total  Time
test_basic_HyperRectangle |   91     91  1.8s
Test Summary:                      | Pass  Total  Time
test_runtests_VectorAffineFunction |   29     29  0.1s
Test Summary:                   | Pass  Total  Time
test_runtests_VectorOfVariables |   29     29  0.1s
Test Summary:                         | Pass  Total  Time
test_runtests_VectorOfVariables_zeros |   29     29  0.0s
Test Summary:          | Pass  Total  Time
test_runtests_free_row |   29     29  0.0s
Test Summary:                | Pass  Total  Time
test_runtests_infinity_lower |   29     29  0.0s
Test Summary:                | Pass  Total  Time
test_runtests_infinity_upper |   29     29  0.0s

[odow]

This needs some better tests. It doesn't account for a few things