increment_trial() was never called — budget enforcement was broken because
TrialBudgetObserver had its own internal Arc<AtomicUsize> disconnected from
the trial_counter used by evaluate_point() and cost(). With num_trials=2,
PSO ran 20 particle evaluations instead of stopping at 2.
Now TrialBudgetObserver::new() takes the caller-owned Arc<AtomicUsize> so
all evaluation paths (LHS via evaluate_point + PSO via cost()) share one
counter. ObjectiveFunction::cost() and ParallelObjectiveFunction::cost()
increment trial_counter directly (fetch_add SeqCst) and check budget inline;
observe_iter() reads the same counter to terminate PSO between iterations.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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