create_counterfactual enhancements (minimization method and fixed features)

Discussed in https://github.com/rasbt/mlxtend/discussions/1028

Originally posted by farbodr April 17, 2023 I have a couple of questions about create_counterfactual?

1. On a small table with the shape of (461, 75) it took about 22 min to return one row. Is there any way to speed this up?
2. Is there any way to limit the features it uses? In other words, can I freeze some features and generate counterfactuals only for some of the features? For instance, in a healthcare use case, we know certain features can not be changed, like a health condition, but there are other features that can be changed that can impact the prediction.

Thanks, FR