fix: add num_proc argument to Dataset.to_sql

[EricSaikali]

Task Done:

• Resolve issue Dataset.to_sql doesn't utilize num_proc #7788 : Add the missing argument mapping in Dataset.to_sql (src/datasets/arrow_dataset.py)

[lhoestq]

Hi ! could you also write a test to make sure this works fine ?

(in case there needs to be a special logic to handle the concurrent writes to the database)