Band Every Score

A teacher turns test scores into bands for school reports:

So 80 is an "A" and 60 is a "B".

Task: write grade_bands(names, scores).

• names and scores are lists of the same length. scores[i] belongs to names[i].
• Build a DataFrame with a name column and a score column, then add a band column.
• Return a dictionary mapping each name to its band, in the original order.

Every name is different, and there is always at least one student.