Offer to help maintain pandarallel #281

Hi Manu, I saw the "looking for a maintainer" note in the README and I'd like to help.

pandarallel is still widely used (~450k downloads/month) and the main pain right now is pandas 2.1+ compatibility. As a start I opened #280, which fixes the DataFrame.applymap deprecation (#258) in a version-safe way that keeps pandas < 2.1 working (addressing the concern raised on #259).

I'm happy to keep clearing the pandas 2.x issues (#254, #255) and to take on ongoing maintenance under your review, including keeping releases and pandas compatibility current. If that's useful I'd be glad to help however works best for you. No rush, and thanks for the library.