BenchmarkSolverFactoryIfc

Creates a fresh solver instance for one benchmark cell, bound to the cell's problem definition and private evaluator.

This is the problem-agnostic counterpart of the concurrent substrate's ksl.simopt.solvers.concurrent.SolverFactoryIfc: a solver case must be able to serve EVERY problem in an experiment, so the problem definition is an argument here rather than something the factory closes over. The benchmark experiment binds the factory to each problem (and wraps it with the budget criterion) before handing it to the concurrent runner.

The substrate factory's contract carries over: return a NEW solver instance on every call, bind it to the supplied evaluator only, and let the solver keep its own fresh stream provider (the solver constructors' default). Implementations are invoked on worker threads, so anything they capture must be safe to read concurrently.