zeta: Send up diagnostics with prediction requests (#24384)

This PR makes it so we send up the diagnostic groups as additional data
with the edit prediction request.

We're not yet making use of them, but we are recording them so we can
use them later (e.g., to train the model).

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/language/src/buffer.rs

@@ -197,7 +197,7 @@ struct SelectionSet {
 }
 
 /// A diagnostic associated with a certain range of a buffer.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Diagnostic {
     /// The name of the service that produced this diagnostic.
     pub source: Option<String>,