mlr3tuning 1.2.0

• feat: Add new callback clbk("mlr3tuning.one_se_rule") that selects the the hyperparameter configuration with the smallest feature set within one standard error of the best.
• feat: Add new stages on_tuning_result_begin and on_result_begin to CallbackAsyncTuning and CallbackBatchTuning.
• refactor: Rename stage on_result to on_result_end in CallbackAsyncTuning and CallbackBatchTuning.
• docs: Extend the CallbackAsyncTuning and CallbackBatchTuning documentation.
• compatibility: mlr3 0.22.0