Please consider jiff support instead of now deprecated chrono.

### Use case

Most of date/datetime manipulations are done through the `chrono` crate (under the `serde` feature). Starting 2026, the `chrono` author said in https://github.com/chronotope/chrono/issues/1768 that the crates are now considered as soft-deprecated, and that [jiff](https://crates.io/crates/jiff) is more or less what we should be using.

### Describe the solution you'd like

Replace all usage of `chrono` with `jiff `:)

Thanks.

Start by searching the repository for all chrono references, including its use under the serde feature, and identify the date/datetime entry points affected by the migration. Review the existing tests around those usages before determining the scope; done means the relevant chrono usage is replaced with jiff without changing supported behavior.

Written by the indexing model from the issue text.