Evaluate jiff for use in example formatting

[daboross]

https://users.rust-lang.org/t/jiff-is-a-new-date-time-library-for-rust-that-encourages-you-to-jump-into-the-pit-of-success/114781

I'm convinced this is worth looking at, at least.

[BurntSushi]

From a quick look, it appears like you could use Jiff in place of both chrono and humantime. Let me know if you have any questions!

[daboross]

Thanks for checking it out!

Yeah will do (ask questions!). I remembered after looking at things that I use chrono in fern itself in a way that exposes its exact strftime format, so I'm going to switch to jiff on a major version.