make JobId (de)serializable — radicle-job

This makes it easier to embed in a struct that gets serialized.

Signed-off-by: Lars Wirzenius liw@liw.fi

 ///
 /// Identifiers can be used to retrieve a [`Job`] or [`JobMut`] through
 /// [`Jobs::get`] and [`Jobs::get_mut`], respectively.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
 pub struct JobId(ObjectId);
 impl JobId {