Ensure Optuna search wrapper is classifier-safe and picklable

[bruAristimunha]

Summary

• add a module-level OptunaSearchCVClassifier wrapper that explicitly marks classifier tags and remains picklable
• simplify optuna search detection while keeping classification-only behavior
• add tests covering classifier tag reporting, pickling, and dict-style tag fallbacks

Testing

• pre-commit run -a
• pytest moabb/tests/test_optuna_wrapper.py

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Codex Task