c722d459

By: Kaapo Seppänen <seppanenkaapo@gmail.com>

resolve the model and warm up once per bench run

Each bench batch called EvaluateSamples::run, which resolved the model
(clone plus recompute_dependents) and warmed up the integrand inside the
timed region. For GL1 that setup was about a quarter of the reported warm
runtime, and its cost grows with the number of model parameters.

with_warmed_integrand now prepares the integrand once; bench times only
run_warmed, the evaluation itself. EvaluateSamples and EvaluateSamplesPrecise
share the helper, so their behaviour is unchanged.