Input dtype

The input dtypes expected by mlflow are int32 although the code uses uint64 consistently.

A temporary workaround is to change the expected dtype to int32, see https://gitlab.sauerburger.com/frank/movie-recommender/-/blob/80b23288e95f3fa65a1122db54ef1164a46547f5/movies.py#L341

The might be related to #5