Guara92 has created PR #587: Add integration with `jiff::Timestamp` in bson-rust

Issue Text:

1. 1. 1. feat: Add interoperability with `jiff::Timestamp`
         Hi!
         This PR introduces interoperability with the `jiff` ([docs](https://docs.rs/jiff/0.2.15/jiff/)) crate by adding helpers to convert between `jiff::Timestamp` and `bson::DateTime`. This allows users of `jiff`, a modern and standards-focused time library, to seamlessly serialize and deserialize timestamps with BSON, I followed the already present integration with `chrono` to add features and tests.

*Changes included:*

• *Optional Dependency*: Added `jiff` as an optional dependency under the `jiff-0_2` feature flag.
• *Serde Helper*: Created a new `serde_with` helper, `datetime::FromJiff02Timestamp`, to enable ergonomic serialization for structs (e.g., `#[serde_as(as = "datetime::FromJiff02Timestamp")]`).
• *Direct Conversions*: Added `DateTime::from_jiff()` and `DateTime::to_jiff()` for direct, manual conversions between the two types.
• *Tests*: Added tests equivalent to the chrono ones

Let me know if I missed anything!