Context. A CSV export double-counted some records — the exact same row appears more than once.
Your task. Write drop_duplicate_rows(df) that returns a DataFrame with duplicate rows removed, keeping the first occurrence of each.
Example. If (Alice, NYC) appears twice, the result keeps just the first one.
Notes. A row is a duplicate only if every column matches. Preserve the order of the rows that are kept. No duplicates → df unchanged.