Replace `chrono` w/ `jiff`

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
Long-term, [`chrono`](https://crates.io/crates/chrono) is likely gonna die. The maintainer [writes](https://dirkjan.ochtman.nl/writing/2026/01/09/reviewing-2025.html):

> To balance out the ongoing adoption of orphaned crates, I'm inclined to wind down maintenance of chrono and chrono-tz in the coming months. The API design for these crates is quite dated, revising it would be a lot of effort, and with [jiff](https://crates.io/crates/jiff) there is now an alternative I feel comfortable recommending.

I think most people would agree that [`jiff`](https://crates.io/crates/jiff) is the cleaner and more future-proof API design. Given that many people love it and it gains more and more traction, I would also expect the performance to be at least as good if not better than [`chrono`](https://crates.io/crates/chrono) at some point.

**Describe the solution you'd like**
Note that this is NOT urgent and more like a mid-/long-term request. However if someone feels they want to pick this up, please go ahead.

Reading through jiff [change log](https://github.com/BurntSushi/jiff/blob/master/CHANGELOG.md) it seems that they are slowly preparing the 1.0 release. We may want to wait for that, but even if 1.0 is a breaking change, I don't expect massive API changes during that release.

**Describe alternatives you've considered**
Not doing anything and just keep the status quo. After all, this isn't urgent.

Or we could use [`time`](https://crates.io/crates/time) even though they have a similar _traditional_ API design (i.e. not the more modern approach that [`jiff`](https://crates.io/crates/jiff) offers):

Compare that w/ [`chrono`](https://crates.io/crates/chrono):

and [`jiff`](https://crates.io/crates/jiff):

**Additional context**
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