Do not always solve child nodes to optimality

[hlefebvr]

Is your feature request related to a problem? Please describe. Currently, all nodes are solved to optimality when they are created. Yet, this is not necessary for correctness. We only need to solve the node optimally if it is selected for branching.

Describe the solution you'd like Nodes should be solved partially according to some criterion (?) and solved only when needed.

Describe alternatives you've considered .

Additional context .