[Optimizers] `"kde"` doesn't exists for surrogate model

[eddiebergman]

First, typo in the error exists -> exist Second, when trying to instantiate "multifidelity_type", I get the following error from instance_from_map()

        if isinstance(request, str):
            if request not in mapping:
>               raise ValueError(f"{request} doesn't exists for {name}")
E               ValueError: kde doesn't exists for surrogate model

This is triggered from here:

neps/optimizers/bayesian_optimization/mf_tpe.py:184: in __init__
    "good": instance_from_map(

Which has the following code:

        self.surrogate_models = {
            "good": instance_from_map(
                SurrogateModelMapping,
                surrogate_model,
                name="surrogate model",
                kwargs=good_model_args,
            ),
            "bad": instance_from_map(
                SurrogateModelMapping,
                surrogate_model,
                name="surrogate model",
                kwargs=surrogate_model_args,
            ),
            "all": instance_from_map(
                SurrogateModelMapping,
                surrogate_model,
                name="surrogate model",
                kwargs=surrogate_model_args,
            ),
        }