Fix in the lowerbound tightening

[dhendryc]

It can happen that both children nodes are pruned. And thus, the lower bound improvement might be substantial for both of them.

Also, corrected the sharpness constants for the optimal design problems according to the corrected proofs.

[matbesancon]

the mac tests failed again:

Sparse poisson regression: Error During Test at /Users/runner/work/Boscia.jl/Boscia.jl/examples/poisson_reg.jl:49
  Got exception outside of a @test
  AssertionError: lower_bound <= tree.incumbent + node.fw_dual_gap_limit : -0.9027271955946277 <= -0.9042653557617399
  Stacktrace:
    [1] evaluate_node!(tree::BnBTree{Boscia.FrankWolfeNode{FrankWolfe.ActiveSet{Vector{Float64}, Float64, Vector{Float64}}, FrankWolfe.DeletedVertexStorage{Vector{Float64}}, Boscia.IntegerBounds, Boscia.NodeInfo{Float64}}, @NamedTuple{problem::Boscia.SimpleOptimizationProblem{var"#f#203"{Float64}, var"#grad!#205"{Float64}, Boscia.TimeTrackingLMO{Boscia.MathOptBLMO{SCIP.Optimizer}}, Boscia.IntegerBounds}, current_node_id::Base.RefValue{Int64}, updated_incumbent::Base.RefValue{Bool}, global_tightening_rhs::Base.RefValue{Float64}, global_tightening_root_info::@NamedTuple{lower_bounds::Dict{Int64, Tuple{Float64, Float64}}, upper_bounds::Dict{Int64, Tuple{Float64, Float64}}}, global_tightenings::Boscia.IntegerBounds, options::Dict{Symbol, Any}, result::Dict{Symbol, Any}}, Vector{Float64}, Boscia.FrankWolfeSolution{Boscia.FrankWolfeNode{FrankWolfe.ActiveSet{Vector{Float64}, Float64, Vector{Float64}}, FrankWolfe.DeletedVertexStorage{Vector{Float64}}, Boscia.IntegerBounds, Boscia.NodeInfo{Float64}}, Vector{Float64}}}, node::Boscia.FrankWolfeNode{FrankWolfe.ActiveSet{Vector{Float64}, Float64, Vector{Float64}}, FrankWolfe.DeletedVertexStorage{Vector{Float64}}, Boscia.IntegerBounds, Boscia.NodeInfo{Float64}})
      @ Boscia ~/work/Boscia.jl/Boscia.jl/src/node.jl:286
    [2] optimize!(tree::BnBTree{Boscia.FrankWolfeNode{FrankWolfe.ActiveSet{Vector{Float64}, Float64, Vector{Float64}}, FrankWolfe.DeletedVertexStorage{Vector{Float64}}, Boscia.IntegerBounds, Boscia.NodeInfo{Float64}}, @NamedTuple{problem::Boscia.SimpleOptimizationProblem{var"#f#203"{Float64}, var"#grad!#205"{Float64}, Boscia.TimeTrackingLMO{Boscia.MathOptBLMO{SCIP.Optimizer}}, Boscia.IntegerBounds}, current_node_id::Base.RefValue{Int64}, updated_incumbent::Base.RefValue{Bool}, global_tightening_rhs::Base.RefValue{Float64}, global_tightening_root_info::@NamedTuple{lower_bounds::Dict{Int64, Tuple{Float64, Float64}}, upper_bounds::Dict{Int64, Tuple{Float64, Float64}}}, global_tightenings::Boscia.IntegerBounds, options::Dict{Symbol, Any}, result::Dict{Symbol, Any}}, Vector{Float64}, Boscia.FrankWolfeSolution{Boscia.FrankWolfeNode{FrankWolfe.ActiveSet{Vector{Float64}, Float64, Vector{Float64}}, FrankWolfe.DeletedVertexStorage{Vector{Float64}}, Boscia.IntegerBounds, Boscia.NodeInfo{Float64}}, Vector{Float64}}}; callback::Boscia.var"#callback#23"{Boscia.var"#callback#20#24"{DateTime, Vector{Float64}, Vector{Float64}, Vector{Float64}, Vector{Int64}, Vector{Int64}, Bool, Vector{Int64}, Vector{Int64}, Vector{Int64}, Dict{Symbol, Any}, Vector{Vector{Int64}}, Vector{Vector{Int64}}, Vector{Vector{Int64}}, Vector{Int64}, Nothing, Vector{Int64}, Vector{Int64}, Vector{Int64}, Int64, Int64, Int64, String, Vector{String}}})
      @ Boscia ~/work/Boscia.jl/Boscia.jl/src/custom_bonobo.jl:35
    [3] solve(f::var"#f#203"{Float64}, grad!::var"#grad!#205"{Float64}, blmo::Boscia.MathOptBLMO{SCIP.Optimizer}; traverse_strategy::Bonobo.BestFirstSearch, branching_strategy::Bonobo.MOST_INFEASIBLE, variant::Boscia.BPCG, line_search::FrankWolfe.Adaptive{Float64, Int64}, active_set::Nothing, lazy::Bool, lazy_tolerance::Float64, fw_epsilon::Float64, verbose::Bool, dual_gap::Float64, rel_dual_gap::Float64, time_limit::Float64, print_iter::Int64, dual_gap_decay_factor::Float64, max_fw_iter::Int64, min_number_lower::Float64, min_node_fw_epsilon::Float64, use_postsolve::Bool, min_fw_iterations::Int64, max_iteration_post::Int64, dual_tightening::Bool, global_dual_tightening::Bool, bnb_callback::Nothing, strong_convexity::Float64, sharpness_constant::Float64, sharpness_exponent::Float64, domain_oracle::Boscia.var"#72#74", start_solution::Nothing, fw_verbose::Bool, use_shadow_set::Bool, custom_heuristics::Vector{Boscia.Heuristic{Boscia.var"#28#29"}}, rounding_prob::Float64, clean_solutions::Bool, max_clean_iter::Int64, kwargs::@Kwargs{})
      @ Boscia ~/work/Boscia.jl/Boscia.jl/src/interface.jl:310
    [4] #solve#70
      @ ~/work/Boscia.jl/Boscia.jl/src/MOI_bounded_oracle.jl:645 [inlined]
    [5] macro expansion
      @ ~/work/Boscia.jl/Boscia.jl/examples/poisson_reg.jl:110 [inlined]
    [6] macro expansion
      @ ~/hostedtoolcache/julia/1.11.1/x64/share/julia/stdlib/v1.11/Test/src/Test.jl:1700 [inlined]
    [7] top-level scope
      @ ~/work/Boscia.jl/Boscia.jl/examples/poisson_reg.jl:50