Resolves Issue 21344: provide a timedelta in a non-string format
- [x] closes #21344
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

This extends the API - and there is a judgement call about how to treat nanosecond-resolution pd.Timedelta() objects in the context of datetime.timedelta() objects.

``Timedelta.resolution`` is used completely internally. rather have you change its name and leave ``.resolution`` as an inherited property. I didn't even know that ``timedelta`` has a property by this name.

This would then be an API change, but conform to ``timedelta``, which we in general want to do. can you rebase closing as stale. if you'd like to continue, pls ping.