Builds on the Solver of #327. method: evolutionary runs a genetic search
for models that aren't smooth: tournament selection, blend crossover and
Gaussian mutation inside the variable bounds, feasibility-first ranking
and integer rounding, then a compass search around the best member. It
stops when the population converges, when the best member stops
improving for a number of generations, or at the evaluation budget. A
seeded generator makes runs repeatable. Population size, mutation rate,
random seed, convergence and Require Bounds are options; the method and
its options are saved in the hidden solver_* names. The Solver
Parameters dialog offers the method.
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