``from_map`` with classes doesn't work

see ``test_from_map_column_projection`` in dask/dask

We hash the function and if this is a class our hashing fails, This might be related to what @fjetter is already looking into

Start with test_from_map_column_projection in dask/dask and reproduce the failure involving from_map with a class. Trace the function-hashing path for class inputs; done means the test passes and class-based from_map column projection works without hashing errors.

Written by the indexing model from the issue text.