The base Tuner class is the class that manages the hyperparameter search process,
including model creation, training, and evaluation. For each trial, a Tuner receives new
hyperparameter values from an Oracle instance. After calling model.fit(...), it
sends the evaluation results back to the Oracle instance and it retrieves the next set
of hyperparameters to try.
There are a few built-in Tuner subclasses available for widely-used tuning
algorithms: RandomSearch, BayesianOptimization and Hyperband.
You can also subclass the Tuner class to customize your tuning process.
In particular, you can override the run_trial function
to customize model building and training.