Implement C Level Timedelta ISO Function; fix JSON usage
- [X] closes #28256
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

similar to @cbertinato great work in #28595 but done deeper in the C extension