PR Permission request for jiff support

[c-git]

Hi,

Thank you very much for this crate. I'm currently using the function excel_to_date_time_object and it turns a type from the chrono library. I'm currently transitioning to the jiff library and there are a few footguns doing the conversion so I'm going to take my time and see what's the best way. I wanted to find out if you'd be amenable to be submitting a PR with the final solution to help the next person. See link below to note from the maintainer of chrono about it's soft deprication.

chronotope/chrono#1301 (comment)

[MathNya]

@c-git
Thank you for your suggestion.
Since we recommend replacing chrono with jiff, umyaspreadsheet must follow suit.

The pull request you’ve proposed is very appealing.
Please go ahead and submit it.

[c-git]

I didn't plan to replace yet as it will take a while for people to transition. So I was thinking add a function, I'll play with the names and you'll give me your feedback. Maybe deprecate the current one and have 2 each named to match the respective library.