extract Optuna from nat-core

[afourniernv]

• Remove optuna dependency from nvidia-nat-core; config_optimizer retains it
• Add SuggestableTrial Protocol to optimizable.py with suggest_categorical, suggest_int, suggest_float methods
• Update SearchSpace.suggest() to accept SuggestableTrial instead of optuna.Trial
• Refresh uv.lock across repo to reflect new dependency graph

Optuna is now a required dependency only in nvidia-nat-config-optimizer. Core uses a structural protocol so any trial-like object (including optuna.Trial) works with SearchSpace.suggest().

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