make `_set_feature_modules` to return `ModuleType` objects

[DaniBodor]

see https://github.com/DeepRank/deeprank2/pull/492#discussion_r1337177705

in query.py # TODO: I would prefer if _set_feature_modules would return a list of ModuleType instead of str, # but this leads to an exception in the pool function in QueryCollection.process, that I don't know how to solve. # Tests are currently passing ModuleTypes directly, which is clearer than passing strings # and is the reason I am allowing both input types.

[github-actions[bot]]

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